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 $96.93   8.293%   $104.9684   $104.97   $104.95   $105.00  
  Purchase #2 $29.96   6.291%   $31.8448   $31.84   $31.85   $31.80  
  Purchase #3 $67.28   13.553%   $76.3985   $76.40   $76.40   $76.40  
  Purchase #4 $228.41   5.639%   $241.29   $241.29   $241.30   $241.30  
  Purchase #5 $69.90   3.487%   $72.3374   $72.34   $72.35   $72.30  
  Purchase #6 $137.81   12.326%   $154.7965   $154.80   $154.80   $154.80  
  Purchase #7 $98.26   8.154%   $106.2721   $106.27   $106.25   $106.30  
  7 purchase totals = $728.55       $787.9077   $787.91   $787.90   $787.90