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 $216.61   8.154%   $234.2724   $234.27   $234.25   $234.30  
  Purchase #2 $14.44   5.177%   $15.1876   $15.19   $15.20   $15.20  
  Purchase #3 $182.59   3.535%   $189.0446   $189.04   $189.05   $189.00  
  Purchase #4 $149.27   12.489%   $167.9123   $167.91   $167.90   $167.90  
  Purchase #5 $45.47   8.494%   $49.3322   $49.33   $49.35   $49.30  
  Purchase #6 $61.39   3.356%   $63.4502   $63.45   $63.45   $63.50  
  Purchase #7 $215.62   9.671%   $236.4726   $236.47   $236.45   $236.50  
  7 purchase totals = $885.39       $955.6719   $955.66   $955.65   $955.70