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 $240.35   10.239%   $264.9594   $264.96   $264.95   $265.00  
  Purchase #2 $227.96   7.708%   $245.5312   $245.53   $245.55   $245.50  
  Purchase #3 $118.68   11.516%   $132.3472   $132.35   $132.35   $132.30  
  Purchase #4 $190.28   12.388%   $213.8519   $213.85   $213.85   $213.90  
  Purchase #5 $190.46   5.609%   $201.1429   $201.14   $201.15   $201.10  
  Purchase #6 $193.78   13.176%   $219.3125   $219.31   $219.30   $219.30  
  Purchase #7 $31.50   12.720%   $35.5068   $35.51   $35.50   $35.50  
  7 purchase totals = $1,193.01       $1,312.6519   $1,312.65   $1,312.65   $1,312.60