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 $61.33   11.690%   $68.4995   $68.50   $68.50   $68.50  
  Purchase #2 $177.91   4.809%   $186.4657   $186.47   $186.45   $186.50  
  Purchase #3 $163.97   11.250%   $182.4166   $182.42   $182.40   $182.40  
  Purchase #4 $71.50   8.835%   $77.817   $77.82   $77.80   $77.80  
  Purchase #5 $53.80   8.307%   $58.2692   $58.27   $58.25   $58.30  
  Purchase #6 $184.38   13.267%   $208.8417   $208.84   $208.85   $208.80  
  Purchase #7 $124.57   6.739%   $132.9648   $132.96   $132.95   $133.00  
  7 purchase totals = $837.46       $915.2745   $915.28   $915.20   $915.30