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 $73.90   6.405%   $78.6333   $78.63   $78.65   $78.60  
  Purchase #2 $182.73   10.325%   $201.5969   $201.60   $201.60   $201.60  
  Purchase #3 $203.42   10.262%   $224.295   $224.30   $224.30   $224.30  
  Purchase #4 $188.49   7.581%   $202.7794   $202.78   $202.80   $202.80  
  Purchase #5 $207.55   8.767%   $225.7459   $225.75   $225.75   $225.70  
  Purchase #6 $61.44   6.550%   $65.4643   $65.46   $65.45   $65.50  
  Purchase #7 $11.36   3.583%   $11.767   $11.77   $11.75   $11.80  
  7 purchase totals = $928.89       $1,010.2818   $1,010.29   $1,010.30   $1,010.30