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 $104.79   8.308%   $113.496   $113.50   $113.50   $113.50  
  Purchase #2 $166.31   8.495%   $180.438   $180.44   $180.45   $180.40  
  Purchase #3 $153.35   9.529%   $167.9627   $167.96   $167.95   $168.00  
  Purchase #4 $190.45   12.745%   $214.7229   $214.72   $214.70   $214.70  
  Purchase #5 $225.82   7.156%   $241.9797   $241.98   $242.00   $242.00  
  Purchase #6 $179.31   9.300%   $195.9858   $195.99   $196.00   $196.00  
  Purchase #7 $223.54   12.867%   $252.3029   $252.30   $252.30   $252.30  
  7 purchase totals = $1,243.57       $1,366.8880   $1,366.89   $1,366.90   $1,366.90