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 $97.49   5.846%   $103.1893   $103.19   $103.20   $103.20  
  Purchase #2 $70.94   8.111%   $76.6939   $76.69   $76.70   $76.70  
  Purchase #3 $71.85   8.114%   $77.6799   $77.68   $77.70   $77.70  
  Purchase #4 $217.95   11.718%   $243.4894   $243.49   $243.50   $243.50  
  Purchase #5 $70.27   8.624%   $76.3301   $76.33   $76.35   $76.30  
  Purchase #6 $46.83   10.495%   $51.7448   $51.74   $51.75   $51.70  
  Purchase #7 $178.65   13.700%   $203.1251   $203.13   $203.15   $203.10  
  7 purchase totals = $753.98       $832.2525   $832.25   $832.35   $832.20