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 $60.83   13.502%   $69.0433   $69.04   $69.05   $69.00  
  Purchase #2 $104.31   11.689%   $116.5028   $116.50   $116.50   $116.50  
  Purchase #3 $183.51   9.500%   $200.9435   $200.94   $200.95   $200.90  
  Purchase #4 $242.86   6.381%   $258.3569   $258.36   $258.35   $258.40  
  Purchase #5 $102.54   4.550%   $107.2056   $107.21   $107.20   $107.20  
  Purchase #6 $46.74   3.265%   $48.2661   $48.27   $48.25   $48.30  
  Purchase #7 $216.49   5.583%   $228.5766   $228.58   $228.60   $228.60  
  7 purchase totals = $957.28       $1,028.8948   $1,028.90   $1,028.90   $1,028.90