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 $152.64   7.280%   $163.7522   $163.75   $163.75   $163.80  
  Purchase #2 $87.35   6.321%   $92.8714   $92.87   $92.85   $92.90  
  Purchase #3 $51.38   5.482%   $54.1967   $54.20   $54.20   $54.20  
  Purchase #4 $176.76   3.386%   $182.7451   $182.75   $182.75   $182.70  
  Purchase #5 $27.87   6.703%   $29.7381   $29.74   $29.75   $29.70  
  Purchase #6 $100.71   10.594%   $111.3792   $111.38   $111.40   $111.40  
  Purchase #7 $106.27   3.129%   $109.5952   $109.60   $109.60   $109.60  
  7 purchase totals = $702.98       $744.2779   $744.29   $744.30   $744.30