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 $23.39   13.301%   $26.5011   $26.50   $26.50   $26.50  
  Purchase #2 $115.60   3.588%   $119.7477   $119.75   $119.75   $119.70  
  Purchase #3 $20.74   5.847%   $21.9527   $21.95   $21.95   $22.00  
  Purchase #4 $148.88   11.603%   $166.1545   $166.15   $166.15   $166.20  
  Purchase #5 $118.59   10.607%   $131.1688   $131.17   $131.15   $131.20  
  Purchase #6 $128.50   5.209%   $135.1936   $135.19   $135.20   $135.20  
  Purchase #7 $146.83   5.585%   $155.0305   $155.03   $155.05   $155.00  
  7 purchase totals = $702.53       $755.7489   $755.74   $755.75   $755.80