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 $182.40   3.625%   $189.012   $189.01   $189.00   $189.00  
  Purchase #2 $170.41   3.336%   $176.0949   $176.09   $176.10   $176.10  
  Purchase #3 $91.97   13.672%   $104.5441   $104.54   $104.55   $104.50  
  Purchase #4 $75.72   10.189%   $83.4351   $83.44   $83.45   $83.40  
  Purchase #5 $12.88   6.411%   $13.7057   $13.71   $13.70   $13.70  
  Purchase #6 $169.67   12.672%   $191.1706   $191.17   $191.15   $191.20  
  Purchase #7 $96.76   12.528%   $108.8821   $108.88   $108.90   $108.90  
  7 purchase totals = $799.81       $866.8445   $866.84   $866.85   $866.80