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 $214.44   13.706%   $243.8311   $243.83   $243.85   $243.80  
  Purchase #2 $248.57   6.197%   $263.9739   $263.97   $263.95   $264.00  
  Purchase #3 $103.37   11.455%   $115.211   $115.21   $115.20   $115.20  
  Purchase #4 $226.98   6.330%   $241.3478   $241.35   $241.35   $241.30  
  Purchase #5 $57.48   6.390%   $61.153   $61.15   $61.15   $61.20  
  Purchase #6 $33.43   13.323%   $37.8839   $37.88   $37.90   $37.90  
  Purchase #7 $237.57   3.194%   $245.158   $245.16   $245.15   $245.20  
  7 purchase totals = $1,121.84       $1,208.5587   $1,208.55   $1,208.55   $1,208.60