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 $59.47   11.688%   $66.4209   $66.42   $66.40   $66.40  
  Purchase #2 $158.84   9.795%   $174.3984   $174.40   $174.40   $174.40  
  Purchase #3 $208.50   3.630%   $216.0686   $216.07   $216.05   $216.10  
  Purchase #4 $55.77   8.366%   $60.4357   $60.44   $60.45   $60.40  
  Purchase #5 $208.96   8.652%   $227.0392   $227.04   $227.05   $227.00  
  Purchase #6 $189.38   12.188%   $212.4616   $212.46   $212.45   $212.50  
  Purchase #7 $211.73   8.531%   $229.7927   $229.79   $229.80   $229.80  
  7 purchase totals = $1,092.65       $1,186.6171   $1,186.62   $1,186.60   $1,186.60