Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $133.82   13.567%   $151.9754   $151.98   $152.00   $152.00  
  Purchase #2 $97.36   11.504%   $108.5603   $108.56   $108.55   $108.60  
  Purchase #3 $214.31   9.216%   $234.0608   $234.06   $234.05   $234.10  
  Purchase #4 $248.94   10.688%   $275.5467   $275.55   $275.55   $275.50  
  Purchase #5 $125.86   13.110%   $142.3602   $142.36   $142.35   $142.40  
  Purchase #6 $141.70   4.154%   $147.5862   $147.59   $147.60   $147.60  
  Purchase #7 $239.35   8.557%   $259.8312   $259.83   $259.85   $259.80  
  7 purchase totals = $1,201.34       $1,319.9208   $1,319.93   $1,319.95   $1,320.00