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 $80.61   13.176%   $91.2312   $91.23   $91.25   $91.20  
  Purchase #2 $215.85   9.677%   $236.7378   $236.74   $236.75   $236.70  
  Purchase #3 $82.83   13.520%   $94.0286   $94.03   $94.05   $94.00  
  Purchase #4 $223.46   9.253%   $244.1368   $244.14   $244.15   $244.10  
  Purchase #5 $197.29   5.687%   $208.5099   $208.51   $208.50   $208.50  
  Purchase #6 $245.90   5.672%   $259.8474   $259.85   $259.85   $259.80  
  Purchase #7 $144.68   4.594%   $151.3266   $151.33   $151.35   $151.30  
  7 purchase totals = $1,190.62       $1,285.8183   $1,285.83   $1,285.90   $1,285.60