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 $162.92   11.812%   $182.1641   $182.16   $182.15   $182.20  
  Purchase #2 $149.99   10.443%   $165.6535   $165.65   $165.65   $165.70  
  Purchase #3 $55.87   10.295%   $61.6218   $61.62   $61.60   $61.60  
  Purchase #4 $232.33   3.302%   $240.0015   $240.00   $240.00   $240.00  
  Purchase #5 $158.52   7.782%   $170.856   $170.86   $170.85   $170.90  
  Purchase #6 $68.32   13.271%   $77.3867   $77.39   $77.40   $77.40  
  Purchase #7 $97.39   9.288%   $106.4356   $106.44   $106.45   $106.40  
  7 purchase totals = $925.34       $1,004.1192   $1,004.12   $1,004.10   $1,004.20