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 $198.87   3.816%   $206.4589   $206.46   $206.45   $206.50  
  Purchase #2 $55.39   3.265%   $57.1985   $57.20   $57.20   $57.20  
  Purchase #3 $248.49   7.281%   $266.5826   $266.58   $266.60   $266.60  
  Purchase #4 $173.54   11.182%   $192.9452   $192.95   $192.95   $192.90  
  Purchase #5 $54.38   10.235%   $59.9458   $59.95   $59.95   $59.90  
  Purchase #6 $217.51   6.457%   $231.5546   $231.55   $231.55   $231.60  
  Purchase #7 $174.28   4.825%   $182.689   $182.69   $182.70   $182.70  
  7 purchase totals = $1,122.46       $1,197.3746   $1,197.38   $1,197.40   $1,197.40