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 $94.82   7.604%   $102.0301   $102.03   $102.05   $102.00  
  Purchase #2 $75.73   3.728%   $78.5532   $78.55   $78.55   $78.60  
  Purchase #3 $243.78   10.353%   $269.0185   $269.02   $269.00   $269.00  
  Purchase #4 $50.84   4.201%   $52.9758   $52.98   $53.00   $53.00  
  Purchase #5 $149.50   13.733%   $170.0308   $170.03   $170.05   $170.00  
  Purchase #6 $16.64   4.631%   $17.4106   $17.41   $17.40   $17.40  
  Purchase #7 $70.63   7.859%   $76.1808   $76.18   $76.20   $76.20  
  7 purchase totals = $701.94       $766.1998   $766.20   $766.25   $766.20