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 $137.91   10.394%   $152.2444   $152.24   $152.25   $152.20  
  Purchase #2 $232.75   4.453%   $243.1144   $243.11   $243.10   $243.10  
  Purchase #3 $68.32   4.293%   $71.253   $71.25   $71.25   $71.30  
  Purchase #4 $93.69   8.281%   $101.4485   $101.45   $101.45   $101.40  
  Purchase #5 $92.76   5.347%   $97.7199   $97.72   $97.70   $97.70  
  Purchase #6 $223.47   4.432%   $233.3742   $233.37   $233.35   $233.40  
  Purchase #7 $31.77   12.156%   $35.632   $35.63   $35.65   $35.60  
  7 purchase totals = $880.67       $934.7864   $934.77   $934.75   $934.70