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 $69.95   3.778%   $72.5927   $72.59   $72.60   $72.60  
  Purchase #2 $25.28   6.263%   $26.8633   $26.86   $26.85   $26.90  
  Purchase #3 $74.55   3.731%   $77.3315   $77.33   $77.35   $77.30  
  Purchase #4 $111.25   4.229%   $115.9548   $115.95   $115.95   $116.00  
  Purchase #5 $37.71   4.694%   $39.4801   $39.48   $39.50   $39.50  
  Purchase #6 $208.96   5.735%   $220.9439   $220.94   $220.95   $220.90  
  Purchase #7 $135.95   6.203%   $144.383   $144.38   $144.40   $144.40  
  7 purchase totals = $663.65       $697.5493   $697.53   $697.60   $697.60