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 $93.66   3.459%   $96.8997   $96.90   $96.90   $96.90  
  Purchase #2 $43.53   8.287%   $47.1373   $47.14   $47.15   $47.10  
  Purchase #3 $76.68   5.234%   $80.6934   $80.69   $80.70   $80.70  
  Purchase #4 $45.58   5.703%   $48.1794   $48.18   $48.20   $48.20  
  Purchase #5 $113.97   3.479%   $117.935   $117.94   $117.95   $117.90  
  Purchase #6 $167.81   8.534%   $182.1309   $182.13   $182.15   $182.10  
  Purchase #7 $184.95   12.132%   $207.3881   $207.39   $207.40   $207.40  
  7 purchase totals = $726.18       $780.3638   $780.37   $780.45   $780.30