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 $233.30   5.795%   $246.8197   $246.82   $246.80   $246.80  
  Purchase #2 $174.38   7.773%   $187.9346   $187.93   $187.95   $187.90  
  Purchase #3 $235.83   13.793%   $268.358   $268.36   $268.35   $268.40  
  Purchase #4 $57.90   9.319%   $63.2957   $63.30   $63.30   $63.30  
  Purchase #5 $114.35   11.650%   $127.6718   $127.67   $127.65   $127.70  
  Purchase #6 $77.85   9.601%   $85.3244   $85.32   $85.30   $85.30  
  Purchase #7 $227.87   8.219%   $246.5986   $246.60   $246.60   $246.60  
  7 purchase totals = $1,121.48       $1,226.0028   $1,226.00   $1,225.95   $1,226.00