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 $63.30   6.206%   $67.2284   $67.23   $67.25   $67.20  
  Purchase #2 $234.62   5.634%   $247.8385   $247.84   $247.85   $247.80  
  Purchase #3 $75.56   10.342%   $83.3744   $83.37   $83.35   $83.40  
  Purchase #4 $180.62   13.290%   $204.6244   $204.62   $204.60   $204.60  
  Purchase #5 $104.80   8.541%   $113.751   $113.75   $113.75   $113.80  
  Purchase #6 $25.79   13.719%   $29.3281   $29.33   $29.35   $29.30  
  Purchase #7 $14.29   12.518%   $16.0788   $16.08   $16.10   $16.10  
  7 purchase totals = $698.98       $762.2236   $762.22   $762.25   $762.20