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 $64.59   4.218%   $67.3144   $67.31   $67.30   $67.30  
  Purchase #2 $126.69   4.611%   $132.5317   $132.53   $132.55   $132.50  
  Purchase #3 $84.87   6.256%   $90.1795   $90.18   $90.20   $90.20  
  Purchase #4 $229.86   7.535%   $247.18   $247.18   $247.20   $247.20  
  Purchase #5 $61.78   4.695%   $64.6806   $64.68   $64.70   $64.70  
  Purchase #6 $249.74   6.281%   $265.4262   $265.43   $265.45   $265.40  
  Purchase #7 $45.60   4.497%   $47.6506   $47.65   $47.65   $47.70  
  7 purchase totals = $863.13       $914.9630   $914.96   $915.05   $915.00