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 $241.96   13.824%   $275.4086   $275.41   $275.40   $275.40  
  Purchase #2 $110.41   6.524%   $117.6131   $117.61   $117.60   $117.60  
  Purchase #3 $87.70   3.128%   $90.4433   $90.44   $90.45   $90.40  
  Purchase #4 $213.38   13.240%   $241.6315   $241.63   $241.65   $241.60  
  Purchase #5 $176.53   4.310%   $184.1384   $184.14   $184.15   $184.10  
  Purchase #6 $174.31   4.770%   $182.6246   $182.62   $182.60   $182.60  
  Purchase #7 $190.29   11.345%   $211.8784   $211.88   $211.90   $211.90  
  7 purchase totals = $1,194.58       $1,303.7379   $1,303.73   $1,303.75   $1,303.60