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 $246.34   8.759%   $267.9169   $267.92   $267.90   $267.90  
  Purchase #2 $59.75   12.731%   $67.3568   $67.36   $67.35   $67.40  
  Purchase #3 $125.61   13.619%   $142.7168   $142.72   $142.70   $142.70  
  Purchase #4 $82.57   13.684%   $93.8689   $93.87   $93.85   $93.90  
  Purchase #5 $160.85   12.353%   $180.7198   $180.72   $180.70   $180.70  
  Purchase #6 $51.91   4.405%   $54.1966   $54.20   $54.20   $54.20  
  Purchase #7 $122.36   11.365%   $136.2662   $136.27   $136.25   $136.30  
  7 purchase totals = $849.39       $943.0420   $943.06   $942.95   $943.10