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 $141.57   3.312%   $146.2588   $146.26   $146.25   $146.30  
  Purchase #2 $33.95   7.142%   $36.3747   $36.37   $36.35   $36.40  
  Purchase #3 $168.85   3.849%   $175.349   $175.35   $175.35   $175.30  
  Purchase #4 $61.47   12.508%   $69.1587   $69.16   $69.15   $69.20  
  Purchase #5 $114.85   4.756%   $120.3123   $120.31   $120.30   $120.30  
  Purchase #6 $166.70   10.779%   $184.6686   $184.67   $184.65   $184.70  
  Purchase #7 $197.87   5.502%   $208.7568   $208.76   $208.75   $208.80  
  7 purchase totals = $885.26       $940.8789   $940.88   $940.80   $941.00