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 $30.71   4.758%   $32.1712   $32.17   $32.15   $32.20  
  Purchase #2 $204.56   10.491%   $226.0204   $226.02   $226.00   $226.00  
  Purchase #3 $91.53   6.823%   $97.7751   $97.78   $97.80   $97.80  
  Purchase #4 $222.56   4.387%   $232.3237   $232.32   $232.30   $232.30  
  Purchase #5 $60.39   4.521%   $63.1202   $63.12   $63.10   $63.10  
  Purchase #6 $50.44   5.373%   $53.1501   $53.15   $53.15   $53.20  
  Purchase #7 $75.80   3.159%   $78.1945   $78.19   $78.20   $78.20  
  7 purchase totals = $735.99       $782.7552   $782.75   $782.70   $782.80