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 $68.54   8.871%   $74.6202   $74.62   $74.60   $74.60  
  Purchase #2 $51.48   6.530%   $54.8416   $54.84   $54.85   $54.80  
  Purchase #3 $92.73   9.135%   $101.2009   $101.20   $101.20   $101.20  
  Purchase #4 $110.89   12.694%   $124.9664   $124.97   $124.95   $125.00  
  Purchase #5 $139.40   8.664%   $151.4776   $151.48   $151.50   $151.50  
  Purchase #6 $162.70   8.609%   $176.7068   $176.71   $176.70   $176.70  
  Purchase #7 $229.40   6.355%   $243.9784   $243.98   $244.00   $244.00  
  7 purchase totals = $855.14       $927.7919   $927.80   $927.80   $927.80