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 $238.75   8.720%   $259.569   $259.57   $259.55   $259.60  
  Purchase #2 $63.97   11.502%   $71.3278   $71.33   $71.35   $71.30  
  Purchase #3 $11.37   5.142%   $11.9546   $11.95   $11.95   $12.00  
  Purchase #4 $13.76   7.783%   $14.8309   $14.83   $14.85   $14.80  
  Purchase #5 $195.29   7.348%   $209.6399   $209.64   $209.65   $209.60  
  Purchase #6 $51.85   10.362%   $57.2227   $57.22   $57.20   $57.20  
  Purchase #7 $123.66   4.584%   $129.3286   $129.33   $129.35   $129.30  
  7 purchase totals = $698.65       $753.8735   $753.87   $753.90   $753.80