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 $13.80   7.820%   $14.8792   $14.88   $14.90   $14.90  
  Purchase #2 $13.68   9.264%   $14.9473   $14.95   $14.95   $14.90  
  Purchase #3 $202.89   5.746%   $214.5481   $214.55   $214.55   $214.50  
  Purchase #4 $116.95   11.544%   $130.4507   $130.45   $130.45   $130.50  
  Purchase #5 $203.81   8.675%   $221.4905   $221.49   $221.50   $221.50  
  Purchase #6 $180.30   7.507%   $193.8351   $193.84   $193.85   $193.80  
  Purchase #7 $125.34   5.664%   $132.4393   $132.44   $132.45   $132.40  
  7 purchase totals = $856.77       $922.5902   $922.60   $922.65   $922.50