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 $56.94   6.412%   $60.591   $60.59   $60.60   $60.60  
  Purchase #2 $86.96   12.293%   $97.65   $97.65   $97.65   $97.70  
  Purchase #3 $37.91   10.338%   $41.8291   $41.83   $41.85   $41.80  
  Purchase #4 $128.26   8.407%   $139.0428   $139.04   $139.05   $139.00  
  Purchase #5 $119.59   4.769%   $125.2932   $125.29   $125.30   $125.30  
  Purchase #6 $144.25   9.528%   $157.9941   $157.99   $158.00   $158.00  
  Purchase #7 $163.91   10.645%   $181.3582   $181.36   $181.35   $181.40  
  7 purchase totals = $737.82       $803.7584   $803.75   $803.80   $803.80