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 $247.74   8.486%   $268.7632   $268.76   $268.75   $268.80  
  Purchase #2 $69.90   8.289%   $75.694   $75.69   $75.70   $75.70  
  Purchase #3 $184.28   13.226%   $208.6529   $208.65   $208.65   $208.70  
  Purchase #4 $245.55   10.725%   $271.8852   $271.89   $271.90   $271.90  
  Purchase #5 $224.72   8.313%   $243.401   $243.40   $243.40   $243.40  
  Purchase #6 $140.26   3.299%   $144.8872   $144.89   $144.90   $144.90  
  Purchase #7 $39.58   7.872%   $42.6957   $42.70   $42.70   $42.70  
  7 purchase totals = $1,152.03       $1,255.9792   $1,255.98   $1,256.00   $1,256.10