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 $55.61   10.805%   $61.6187   $61.62   $61.60   $61.60  
  Purchase #2 $221.30   11.709%   $247.212   $247.21   $247.20   $247.20  
  Purchase #3 $194.69   13.342%   $220.6655   $220.67   $220.65   $220.70  
  Purchase #4 $5.48   9.294%   $5.9893   $5.99   $6.00   $6.00  
  Purchase #5 $98.96   5.477%   $104.38   $104.38   $104.40   $104.40  
  Purchase #6 $86.78   6.869%   $92.7409   $92.74   $92.75   $92.70  
  Purchase #7 $201.94   3.452%   $208.911   $208.91   $208.90   $208.90  
  7 purchase totals = $864.76       $941.5174   $941.52   $941.50   $941.50