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 $23.85   7.353%   $25.6037   $25.60   $25.60   $25.60  
  Purchase #2 $56.98   3.391%   $58.9122   $58.91   $58.90   $58.90  
  Purchase #3 $14.50   8.357%   $15.7118   $15.71   $15.70   $15.70  
  Purchase #4 $60.31   8.341%   $65.3405   $65.34   $65.35   $65.30  
  Purchase #5 $248.53   4.517%   $259.7561   $259.76   $259.75   $259.80  
  Purchase #6 $128.57   11.755%   $143.6834   $143.68   $143.70   $143.70  
  Purchase #7 $209.86   11.735%   $234.4871   $234.49   $234.50   $234.50  
  7 purchase totals = $742.60       $803.4948   $803.49   $803.50   $803.50