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 $182.70   6.182%   $193.9945   $193.99   $194.00   $194.00  
  Purchase #2 $92.59   11.221%   $102.9795   $102.98   $103.00   $103.00  
  Purchase #3 $149.64   9.315%   $163.579   $163.58   $163.60   $163.60  
  Purchase #4 $85.61   11.643%   $95.5776   $95.58   $95.60   $95.60  
  Purchase #5 $53.82   7.616%   $57.9189   $57.92   $57.90   $57.90  
  Purchase #6 $135.87   13.692%   $154.4733   $154.47   $154.45   $154.50  
  Purchase #7 $65.51   13.202%   $74.1586   $74.16   $74.15   $74.20  
  7 purchase totals = $765.74       $842.6814   $842.68   $842.70   $842.80