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 $57.51   9.298%   $62.8573   $62.86   $62.85   $62.90  
  Purchase #2 $174.35   10.784%   $193.1519   $193.15   $193.15   $193.20  
  Purchase #3 $61.90   4.142%   $64.4639   $64.46   $64.45   $64.50  
  Purchase #4 $195.85   5.559%   $206.7373   $206.74   $206.75   $206.70  
  Purchase #5 $22.30   11.714%   $24.9122   $24.91   $24.90   $24.90  
  Purchase #6 $201.96   12.652%   $227.512   $227.51   $227.50   $227.50  
  Purchase #7 $122.48   12.538%   $137.8365   $137.84   $137.85   $137.80  
  7 purchase totals = $836.35       $917.4711   $917.47   $917.45   $917.50