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 $29.29   13.691%   $33.3001   $33.30   $33.30   $33.30  
  Purchase #2 $248.61   6.786%   $265.4807   $265.48   $265.50   $265.50  
  Purchase #3 $155.73   7.109%   $166.8008   $166.80   $166.80   $166.80  
  Purchase #4 $132.45   3.601%   $137.2195   $137.22   $137.20   $137.20  
  Purchase #5 $105.59   6.630%   $112.5906   $112.59   $112.60   $112.60  
  Purchase #6 $61.29   4.340%   $63.95   $63.95   $63.95   $64.00  
  Purchase #7 $211.94   9.579%   $232.2417   $232.24   $232.25   $232.20  
  7 purchase totals = $944.90       $1,011.5834   $1,011.58   $1,011.60   $1,011.60