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 $228.91   8.113%   $247.4815   $247.48   $247.50   $247.50  
  Purchase #2 $214.67   13.300%   $243.2211   $243.22   $243.20   $243.20  
  Purchase #3 $46.57   7.182%   $49.9147   $49.91   $49.90   $49.90  
  Purchase #4 $153.41   13.189%   $173.6432   $173.64   $173.65   $173.60  
  Purchase #5 $180.60   7.418%   $193.9969   $194.00   $194.00   $194.00  
  Purchase #6 $166.26   3.593%   $172.2337   $172.23   $172.25   $172.20  
  Purchase #7 $181.93   6.732%   $194.1775   $194.18   $194.20   $194.20  
  7 purchase totals = $1,172.35       $1,274.6686   $1,274.66   $1,274.70   $1,274.60