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 $43.56   6.792%   $46.5186   $46.52   $46.50   $46.50  
  Purchase #2 $215.76   5.423%   $227.4607   $227.46   $227.45   $227.50  
  Purchase #3 $244.54   7.431%   $262.7118   $262.71   $262.70   $262.70  
  Purchase #4 $160.41   5.481%   $169.2021   $169.20   $169.20   $169.20  
  Purchase #5 $169.47   6.228%   $180.0246   $180.02   $180.00   $180.00  
  Purchase #6 $208.77   11.582%   $232.9497   $232.95   $232.95   $232.90  
  Purchase #7 $176.60   5.811%   $186.8622   $186.86   $186.85   $186.90  
  7 purchase totals = $1,219.11       $1,305.7297   $1,305.72   $1,305.65   $1,305.70