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 $217.51   13.698%   $247.3045   $247.30   $247.30   $247.30  
  Purchase #2 $54.67   9.221%   $59.7111   $59.71   $59.70   $59.70  
  Purchase #3 $119.49   4.426%   $124.7786   $124.78   $124.80   $124.80  
  Purchase #4 $27.52   6.577%   $29.33   $29.33   $29.35   $29.30  
  Purchase #5 $206.94   5.553%   $218.4314   $218.43   $218.45   $218.40  
  Purchase #6 $184.79   12.600%   $208.0735   $208.07   $208.05   $208.10  
  Purchase #7 $49.45   8.600%   $53.7027   $53.70   $53.70   $53.70  
  7 purchase totals = $860.37       $941.3318   $941.32   $941.35   $941.30