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 $50.29   4.835%   $52.7215   $52.72   $52.70   $52.70  
  Purchase #2 $194.78   9.504%   $213.2919   $213.29   $213.30   $213.30  
  Purchase #3 $101.35   5.415%   $106.8381   $106.84   $106.85   $106.80  
  Purchase #4 $68.65   5.316%   $72.2994   $72.30   $72.30   $72.30  
  Purchase #5 $180.48   4.812%   $189.1647   $189.16   $189.15   $189.20  
  Purchase #6 $26.82   7.639%   $28.8688   $28.87   $28.85   $28.90  
  Purchase #7 $226.65   11.633%   $253.0162   $253.02   $253.00   $253.00  
  7 purchase totals = $849.02       $916.2006   $916.20   $916.15   $916.20