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 $22.28   10.252%   $24.5641   $24.56   $24.55   $24.60  
  Purchase #2 $119.53   12.839%   $134.8765   $134.88   $134.90   $134.90  
  Purchase #3 $82.39   12.466%   $92.6607   $92.66   $92.65   $92.70  
  Purchase #4 $20.27   10.327%   $22.3633   $22.36   $22.35   $22.40  
  Purchase #5 $162.51   13.414%   $184.3091   $184.31   $184.30   $184.30  
  Purchase #6 $53.87   8.572%   $58.4877   $58.49   $58.50   $58.50  
  Purchase #7 $102.43   13.558%   $116.3175   $116.32   $116.30   $116.30  
  7 purchase totals = $563.28       $633.5789   $633.58   $633.55   $633.70