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 $202.96   11.793%   $226.8951   $226.90   $226.90   $226.90  
  Purchase #2 $206.54   3.359%   $213.4777   $213.48   $213.50   $213.50  
  Purchase #3 $156.43   13.317%   $177.2618   $177.26   $177.25   $177.30  
  Purchase #4 $240.33   8.248%   $260.1524   $260.15   $260.15   $260.20  
  Purchase #5 $147.87   9.562%   $162.0093   $162.01   $162.00   $162.00  
  Purchase #6 $233.72   13.787%   $265.943   $265.94   $265.95   $265.90  
  Purchase #7 $67.52   13.641%   $76.7304   $76.73   $76.75   $76.70  
  7 purchase totals = $1,255.37       $1,382.4697   $1,382.47   $1,382.50   $1,382.50