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 $190.69   4.254%   $198.802   $198.80   $198.80   $198.80  
  Purchase #2 $22.33   5.268%   $23.5063   $23.51   $23.50   $23.50  
  Purchase #3 $58.38   11.677%   $65.197   $65.20   $65.20   $65.20  
  Purchase #4 $67.47   8.276%   $73.0538   $73.05   $73.05   $73.10  
  Purchase #5 $153.44   8.461%   $166.4226   $166.42   $166.40   $166.40  
  Purchase #6 $138.39   4.525%   $144.6521   $144.65   $144.65   $144.70  
  Purchase #7 $233.52   13.866%   $265.8999   $265.90   $265.90   $265.90  
  7 purchase totals = $864.22       $937.5337   $937.53   $937.50   $937.60