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 $91.46   11.313%   $101.8069   $101.81   $101.80   $101.80  
  Purchase #2 $112.81   12.305%   $126.6913   $126.69   $126.70   $126.70  
  Purchase #3 $64.60   4.743%   $67.664   $67.66   $67.65   $67.70  
  Purchase #4 $186.87   10.777%   $207.009   $207.01   $207.00   $207.00  
  Purchase #5 $129.58   8.292%   $140.3248   $140.32   $140.30   $140.30  
  Purchase #6 $8.40   8.738%   $9.134   $9.13   $9.15   $9.10  
  Purchase #7 $143.70   6.212%   $152.6266   $152.63   $152.65   $152.60  
  7 purchase totals = $737.42       $805.2566   $805.25   $805.25   $805.20