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 $23.35   9.722%   $25.6201   $25.62   $25.60   $25.60  
  Purchase #2 $189.75   3.733%   $196.8334   $196.83   $196.85   $196.80  
  Purchase #3 $11.65   4.441%   $12.1674   $12.17   $12.15   $12.20  
  Purchase #4 $228.41   4.639%   $239.0059   $239.01   $239.00   $239.00  
  Purchase #5 $57.98   5.386%   $61.1028   $61.10   $61.10   $61.10  
  Purchase #6 $44.83   10.824%   $49.6824   $49.68   $49.70   $49.70  
  Purchase #7 $152.95   8.600%   $166.1037   $166.10   $166.10   $166.10  
  7 purchase totals = $708.92       $750.5157   $750.51   $750.50   $750.50