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 $203.66   6.809%   $217.5272   $217.53   $217.55   $217.50  
  Purchase #2 $153.41   12.513%   $172.6062   $172.61   $172.60   $172.60  
  Purchase #3 $111.95   9.665%   $122.77   $122.77   $122.75   $122.80  
  Purchase #4 $59.55   7.585%   $64.0669   $64.07   $64.05   $64.10  
  Purchase #5 $250.65   6.452%   $266.8219   $266.82   $266.80   $266.80  
  Purchase #6 $50.77   13.483%   $57.6153   $57.62   $57.60   $57.60  
  Purchase #7 $69.74   7.457%   $74.9405   $74.94   $74.95   $74.90  
  7 purchase totals = $899.73       $976.3480   $976.36   $976.30   $976.30