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 $67.90   12.200%   $76.1838   $76.18   $76.20   $76.20  
  Purchase #2 $71.84   11.691%   $80.2388   $80.24   $80.25   $80.20  
  Purchase #3 $125.28   9.736%   $137.4773   $137.48   $137.50   $137.50  
  Purchase #4 $236.96   13.495%   $268.9378   $268.94   $268.95   $268.90  
  Purchase #5 $65.79   10.234%   $72.5229   $72.52   $72.50   $72.50  
  Purchase #6 $250.83   4.789%   $262.8422   $262.84   $262.85   $262.80  
  Purchase #7 $45.79   6.866%   $48.9339   $48.93   $48.95   $48.90  
  7 purchase totals = $864.39       $947.1367   $947.13   $947.20   $947.00