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 $154.92   5.161%   $162.9154   $162.92   $162.90   $162.90  
  Purchase #2 $63.38   7.173%   $67.9262   $67.93   $67.95   $67.90  
  Purchase #3 $217.30   12.330%   $244.0931   $244.09   $244.10   $244.10  
  Purchase #4 $157.98   6.710%   $168.5805   $168.58   $168.60   $168.60  
  Purchase #5 $8.77   5.415%   $9.2449   $9.24   $9.25   $9.20  
  Purchase #6 $114.27   8.519%   $124.0047   $124.00   $124.00   $124.00  
  Purchase #7 $196.84   5.559%   $207.7823   $207.78   $207.80   $207.80  
  7 purchase totals = $913.46       $984.5471   $984.54   $984.60   $984.50