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 $22.84   8.652%   $24.8161   $24.82   $24.80   $24.80  
  Purchase #2 $104.27   10.558%   $115.2788   $115.28   $115.30   $115.30  
  Purchase #3 $87.88   10.829%   $97.3965   $97.40   $97.40   $97.40  
  Purchase #4 $60.46   10.775%   $66.9746   $66.97   $66.95   $67.00  
  Purchase #5 $193.43   6.346%   $205.7051   $205.71   $205.70   $205.70  
  Purchase #6 $160.79   9.579%   $176.1921   $176.19   $176.20   $176.20  
  Purchase #7 $78.99   8.380%   $85.6094   $85.61   $85.60   $85.60  
  7 purchase totals = $708.66       $771.9726   $771.98   $771.95   $772.00