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 $248.38   10.742%   $275.061   $275.06   $275.05   $275.10  
  Purchase #2 $168.34   11.213%   $187.216   $187.22   $187.20   $187.20  
  Purchase #3 $159.42   6.510%   $169.7982   $169.80   $169.80   $169.80  
  Purchase #4 $204.95   6.239%   $217.7368   $217.74   $217.75   $217.70  
  Purchase #5 $81.37   5.258%   $85.6484   $85.65   $85.65   $85.60  
  Purchase #6 $225.88   5.260%   $237.7613   $237.76   $237.75   $237.80  
  Purchase #7 $12.50   3.362%   $12.9203   $12.92   $12.90   $12.90  
  7 purchase totals = $1,100.84       $1,186.1420   $1,186.15   $1,186.10   $1,186.10