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 $120.51   10.172%   $132.7683   $132.77   $132.75   $132.80  
  Purchase #2 $94.98   11.477%   $105.8809   $105.88   $105.90   $105.90  
  Purchase #3 $181.73   7.552%   $195.4542   $195.45   $195.45   $195.50  
  Purchase #4 $207.82   3.740%   $215.5925   $215.59   $215.60   $215.60  
  Purchase #5 $35.94   13.403%   $40.757   $40.76   $40.75   $40.80  
  Purchase #6 $228.67   11.177%   $254.2284   $254.23   $254.25   $254.20  
  Purchase #7 $193.89   5.395%   $204.3504   $204.35   $204.35   $204.40  
  7 purchase totals = $1,063.54       $1,149.0317   $1,149.03   $1,149.05   $1,149.20