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 $214.59   6.423%   $228.3731   $228.37   $228.35   $228.40  
  Purchase #2 $108.42   4.807%   $113.6317   $113.63   $113.65   $113.60  
  Purchase #3 $206.70   4.455%   $215.9085   $215.91   $215.90   $215.90  
  Purchase #4 $40.95   10.213%   $45.1322   $45.13   $45.15   $45.10  
  Purchase #5 $103.52   7.846%   $111.6422   $111.64   $111.65   $111.60  
  Purchase #6 $64.50   5.713%   $68.1849   $68.18   $68.20   $68.20  
  Purchase #7 $143.97   11.607%   $160.6806   $160.68   $160.70   $160.70  
  7 purchase totals = $882.65       $943.5532   $943.54   $943.60   $943.50