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 $210.27   5.874%   $222.6213   $222.62   $222.60   $222.60  
  Purchase #2 $213.78   13.155%   $241.9028   $241.90   $241.90   $241.90  
  Purchase #3 $116.55   9.240%   $127.3192   $127.32   $127.30   $127.30  
  Purchase #4 $75.59   12.413%   $84.973   $84.97   $84.95   $85.00  
  Purchase #5 $47.44   7.405%   $50.9529   $50.95   $50.95   $51.00  
  Purchase #6 $52.80   10.354%   $58.2669   $58.27   $58.25   $58.30  
  Purchase #7 $171.25   12.137%   $192.0346   $192.03   $192.05   $192.00  
  7 purchase totals = $887.68       $978.0707   $978.06   $978.00   $978.10