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 $66.93   12.385%   $75.2193   $75.22   $75.20   $75.20  
  Purchase #2 $144.45   5.864%   $152.9205   $152.92   $152.90   $152.90  
  Purchase #3 $70.38   6.122%   $74.6887   $74.69   $74.70   $74.70  
  Purchase #4 $238.36   5.472%   $251.4031   $251.40   $251.40   $251.40  
  Purchase #5 $107.85   4.726%   $112.947   $112.95   $112.95   $112.90  
  Purchase #6 $240.86   6.237%   $255.8824   $255.88   $255.90   $255.90  
  Purchase #7 $232.70   4.620%   $243.4507   $243.45   $243.45   $243.50  
  7 purchase totals = $1,101.53       $1,166.5117   $1,166.51   $1,166.50   $1,166.50