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 $138.76   5.509%   $146.4043   $146.40   $146.40   $146.40  
  Purchase #2 $144.47   4.345%   $150.7472   $150.75   $150.75   $150.70  
  Purchase #3 $54.54   10.777%   $60.4178   $60.42   $60.40   $60.40  
  Purchase #4 $118.31   5.454%   $124.7626   $124.76   $124.75   $124.80  
  Purchase #5 $217.62   11.170%   $241.9282   $241.93   $241.95   $241.90  
  Purchase #6 $174.89   13.288%   $198.1294   $198.13   $198.15   $198.10  
  Purchase #7 $59.76   6.104%   $63.4078   $63.41   $63.40   $63.40  
  7 purchase totals = $908.35       $985.7973   $985.80   $985.80   $985.70