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 $62.86   10.123%   $69.2233   $69.22   $69.20   $69.20  
  Purchase #2 $157.72   8.345%   $170.8817   $170.88   $170.90   $170.90  
  Purchase #3 $52.89   10.504%   $58.4456   $58.45   $58.45   $58.40  
  Purchase #4 $183.74   10.672%   $203.3487   $203.35   $203.35   $203.30  
  Purchase #5 $199.32   13.180%   $225.5904   $225.59   $225.60   $225.60  
  Purchase #6 $17.53   4.689%   $18.352   $18.35   $18.35   $18.40  
  Purchase #7 $50.89   11.212%   $56.5958   $56.60   $56.60   $56.60  
  7 purchase totals = $724.95       $802.4375   $802.44   $802.45   $802.40