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 $59.61   12.825%   $67.255   $67.26   $67.25   $67.30  
  Purchase #2 $218.41   5.220%   $229.811   $229.81   $229.80   $229.80  
  Purchase #3 $154.45   10.453%   $170.5947   $170.59   $170.60   $170.60  
  Purchase #4 $224.28   12.640%   $252.629   $252.63   $252.65   $252.60  
  Purchase #5 $218.44   10.568%   $241.5247   $241.52   $241.50   $241.50  
  Purchase #6 $232.50   11.302%   $258.7772   $258.78   $258.80   $258.80  
  Purchase #7 $78.31   7.216%   $83.9608   $83.96   $83.95   $84.00  
  7 purchase totals = $1,186.00       $1,304.5524   $1,304.55   $1,304.55   $1,304.60