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 $58.68   11.659%   $65.5215   $65.52   $65.50   $65.50  
  Purchase #2 $186.98   8.147%   $202.2133   $202.21   $202.20   $202.20  
  Purchase #3 $47.95   7.775%   $51.6781   $51.68   $51.70   $51.70  
  Purchase #4 $41.56   11.161%   $46.1985   $46.20   $46.20   $46.20  
  Purchase #5 $220.61   10.131%   $242.96   $242.96   $242.95   $243.00  
  Purchase #6 $54.96   12.427%   $61.7899   $61.79   $61.80   $61.80  
  Purchase #7 $70.40   4.227%   $73.3758   $73.38   $73.40   $73.40  
  7 purchase totals = $681.14       $743.7371   $743.74   $743.75   $743.80