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 $59.36   13.835%   $67.5725   $67.57   $67.55   $67.60  
  Purchase #2 $61.94   7.275%   $66.4461   $66.45   $66.45   $66.40  
  Purchase #3 $18.79   3.627%   $19.4715   $19.47   $19.45   $19.50  
  Purchase #4 $58.51   9.814%   $64.2522   $64.25   $64.25   $64.30  
  Purchase #5 $8.29   3.274%   $8.5614   $8.56   $8.55   $8.60  
  Purchase #6 $114.55   4.778%   $120.0232   $120.02   $120.00   $120.00  
  Purchase #7 $153.74   9.277%   $168.0025   $168.00   $168.00   $168.00  
  7 purchase totals = $475.18       $514.3294   $514.32   $514.25   $514.40