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 $217.67   13.843%   $247.8021   $247.80   $247.80   $247.80  
  Purchase #2 $180.72   7.701%   $194.6372   $194.64   $194.65   $194.60  
  Purchase #3 $214.55   9.293%   $234.4881   $234.49   $234.50   $234.50  
  Purchase #4 $43.43   7.135%   $46.5287   $46.53   $46.55   $46.50  
  Purchase #5 $30.63   5.114%   $32.1964   $32.20   $32.20   $32.20  
  Purchase #6 $46.48   10.424%   $51.3251   $51.33   $51.35   $51.30  
  Purchase #7 $70.50   4.311%   $73.5393   $73.54   $73.55   $73.50  
  7 purchase totals = $803.98       $880.5169   $880.53   $880.60   $880.40