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 $218.89   11.207%   $243.421   $243.42   $243.40   $243.40  
  Purchase #2 $110.73   6.566%   $118.0005   $118.00   $118.00   $118.00  
  Purchase #3 $195.77   7.800%   $211.0401   $211.04   $211.05   $211.00  
  Purchase #4 $162.37   6.716%   $173.2748   $173.27   $173.25   $173.30  
  Purchase #5 $195.61   4.583%   $204.5748   $204.57   $204.55   $204.60  
  Purchase #6 $137.87   10.118%   $151.8197   $151.82   $151.80   $151.80  
  Purchase #7 $248.45   10.667%   $274.9522   $274.95   $274.95   $275.00  
  7 purchase totals = $1,269.69       $1,377.0831   $1,377.07   $1,377.00   $1,377.10