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 $235.48   10.420%   $260.017   $260.02   $260.00   $260.00  
  Purchase #2 $50.30   3.437%   $52.0288   $52.03   $52.05   $52.00  
  Purchase #3 $178.62   9.306%   $195.2424   $195.24   $195.25   $195.20  
  Purchase #4 $56.64   4.752%   $59.3315   $59.33   $59.35   $59.30  
  Purchase #5 $216.59   9.244%   $236.6116   $236.61   $236.60   $236.60  
  Purchase #6 $173.81   9.471%   $190.2715   $190.27   $190.25   $190.30  
  Purchase #7 $211.56   8.245%   $229.0031   $229.00   $229.00   $229.00  
  7 purchase totals = $1,123.00       $1,222.5059   $1,222.50   $1,222.50   $1,222.40