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 $57.88   5.222%   $60.9025   $60.90   $60.90   $60.90  
  Purchase #2 $227.44   4.134%   $236.8424   $236.84   $236.85   $236.80  
  Purchase #3 $188.79   8.682%   $205.1807   $205.18   $205.20   $205.20  
  Purchase #4 $233.37   10.776%   $258.518   $258.52   $258.50   $258.50  
  Purchase #5 $54.81   13.571%   $62.2483   $62.25   $62.25   $62.20  
  Purchase #6 $250.45   4.699%   $262.2186   $262.22   $262.20   $262.20  
  Purchase #7 $196.75   13.870%   $224.0392   $224.04   $224.05   $224.00  
  7 purchase totals = $1,209.49       $1,309.9497   $1,309.95   $1,309.95   $1,309.80