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 $46.79   12.255%   $52.5241   $52.52   $52.50   $52.50  
  Purchase #2 $228.42   3.665%   $236.7916   $236.79   $236.80   $236.80  
  Purchase #3 $66.50   10.781%   $73.6694   $73.67   $73.65   $73.70  
  Purchase #4 $237.31   13.299%   $268.8699   $268.87   $268.85   $268.90  
  Purchase #5 $109.75   7.181%   $117.6311   $117.63   $117.65   $117.60  
  Purchase #6 $55.74   10.766%   $61.741   $61.74   $61.75   $61.70  
  Purchase #7 $145.72   6.279%   $154.8698   $154.87   $154.85   $154.90  
  7 purchase totals = $890.23       $966.0969   $966.09   $966.05   $966.10