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 $62.71   7.153%   $67.1956   $67.20   $67.20   $67.20  
  Purchase #2 $75.83   8.853%   $82.5432   $82.54   $82.55   $82.50  
  Purchase #3 $113.38   13.316%   $128.4777   $128.48   $128.50   $128.50  
  Purchase #4 $246.36   6.535%   $262.4596   $262.46   $262.45   $262.50  
  Purchase #5 $142.35   12.326%   $159.8961   $159.90   $159.90   $159.90  
  Purchase #6 $108.80   11.339%   $121.1368   $121.14   $121.15   $121.10  
  Purchase #7 $50.98   12.176%   $57.1873   $57.19   $57.20   $57.20  
  7 purchase totals = $800.41       $878.8963   $878.91   $878.95   $878.90