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 $61.67   6.282%   $65.5441   $65.54   $65.55   $65.50  
  Purchase #2 $104.29   7.591%   $112.2067   $112.21   $112.20   $112.20  
  Purchase #3 $61.94   5.414%   $65.2934   $65.29   $65.30   $65.30  
  Purchase #4 $83.40   5.541%   $88.0212   $88.02   $88.00   $88.00  
  Purchase #5 $112.45   12.539%   $126.5501   $126.55   $126.55   $126.60  
  Purchase #6 $124.84   10.324%   $137.7285   $137.73   $137.75   $137.70  
  Purchase #7 $51.91   10.869%   $57.5521   $57.55   $57.55   $57.60  
  7 purchase totals = $600.50       $652.8961   $652.89   $652.90   $652.90