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 $66.79   13.732%   $75.9616   $75.96   $75.95   $76.00  
  Purchase #2 $206.94   11.339%   $230.4049   $230.40   $230.40   $230.40  
  Purchase #3 $106.37   10.874%   $117.9367   $117.94   $117.95   $117.90  
  Purchase #4 $60.51   8.428%   $65.6098   $65.61   $65.60   $65.60  
  Purchase #5 $223.94   8.783%   $243.6087   $243.61   $243.60   $243.60  
  Purchase #6 $84.89   12.642%   $95.6218   $95.62   $95.60   $95.60  
  Purchase #7 $21.74   8.674%   $23.6257   $23.63   $23.65   $23.60  
  7 purchase totals = $771.18       $852.7692   $852.77   $852.75   $852.70