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 $233.62   12.373%   $262.5258   $262.53   $262.55   $262.50  
  Purchase #2 $164.26   5.768%   $173.7345   $173.73   $173.75   $173.70  
  Purchase #3 $34.94   11.479%   $38.9508   $38.95   $38.95   $39.00  
  Purchase #4 $234.65   3.687%   $243.3015   $243.30   $243.30   $243.30  
  Purchase #5 $244.93   12.562%   $275.6981   $275.70   $275.70   $275.70  
  Purchase #6 $117.63   13.239%   $133.203   $133.20   $133.20   $133.20  
  Purchase #7 $69.84   4.675%   $73.105   $73.11   $73.10   $73.10  
  7 purchase totals = $1,099.87       $1,200.5187   $1,200.52   $1,200.55   $1,200.50