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 $23.92   10.694%   $26.478   $26.48   $26.50   $26.50  
  Purchase #2 $60.51   10.384%   $66.7934   $66.79   $66.80   $66.80  
  Purchase #3 $249.96   9.141%   $272.8088   $272.81   $272.80   $272.80  
  Purchase #4 $218.89   10.298%   $241.4313   $241.43   $241.45   $241.40  
  Purchase #5 $177.32   6.535%   $188.9079   $188.91   $188.90   $188.90  
  Purchase #6 $170.47   9.649%   $186.9187   $186.92   $186.90   $186.90  
  Purchase #7 $84.94   5.249%   $89.3985   $89.40   $89.40   $89.40  
  7 purchase totals = $986.01       $1,072.7366   $1,072.74   $1,072.75   $1,072.70