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 $136.68   7.295%   $146.6508   $146.65   $146.65   $146.70  
  Purchase #2 $195.99   7.838%   $211.3517   $211.35   $211.35   $211.40  
  Purchase #3 $239.89   11.815%   $268.233   $268.23   $268.25   $268.20  
  Purchase #4 $30.32   12.269%   $34.04   $34.04   $34.05   $34.00  
  Purchase #5 $11.85   4.412%   $12.3728   $12.37   $12.35   $12.40  
  Purchase #6 $111.78   5.133%   $117.5177   $117.52   $117.50   $117.50  
  Purchase #7 $14.97   3.315%   $15.4663   $15.47   $15.45   $15.50  
  7 purchase totals = $741.48       $805.6323   $805.63   $805.60   $805.70