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 $53.68   10.263%   $59.1892   $59.19   $59.20   $59.20  
  Purchase #2 $234.68   12.380%   $263.7334   $263.73   $263.75   $263.70  
  Purchase #3 $126.37   10.474%   $139.606   $139.61   $139.60   $139.60  
  Purchase #4 $18.50   4.615%   $19.3538   $19.35   $19.35   $19.40  
  Purchase #5 $165.50   3.561%   $171.3935   $171.39   $171.40   $171.40  
  Purchase #6 $241.88   10.437%   $267.125   $267.13   $267.15   $267.10  
  Purchase #7 $105.99   11.290%   $117.9563   $117.96   $117.95   $118.00  
  7 purchase totals = $946.60       $1,038.3572   $1,038.36   $1,038.40   $1,038.40