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 $85.63   10.196%   $94.3608   $94.36   $94.35   $94.40  
  Purchase #2 $231.45   9.547%   $253.5465   $253.55   $253.55   $253.50  
  Purchase #3 $239.89   5.751%   $253.6861   $253.69   $253.70   $253.70  
  Purchase #4 $21.31   7.673%   $22.9451   $22.95   $22.95   $22.90  
  Purchase #5 $65.36   5.740%   $69.1117   $69.11   $69.10   $69.10  
  Purchase #6 $37.36   10.208%   $41.1737   $41.17   $41.15   $41.20  
  Purchase #7 $66.71   4.274%   $69.5612   $69.56   $69.55   $69.60  
  7 purchase totals = $747.71       $804.3851   $804.39   $804.35   $804.40