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 $118.52   13.332%   $134.3211   $134.32   $134.30   $134.30  
  Purchase #2 $135.63   3.631%   $140.5547   $140.55   $140.55   $140.60  
  Purchase #3 $153.39   10.488%   $169.4775   $169.48   $169.50   $169.50  
  Purchase #4 $200.67   3.521%   $207.7356   $207.74   $207.75   $207.70  
  Purchase #5 $153.55   6.189%   $163.0532   $163.05   $163.05   $163.10  
  Purchase #6 $75.59   9.542%   $82.8028   $82.80   $82.80   $82.80  
  Purchase #7 $55.67   5.248%   $58.5916   $58.59   $58.60   $58.60  
  7 purchase totals = $893.02       $956.5365   $956.53   $956.55   $956.60