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 $69.39   10.167%   $76.4449   $76.44   $76.45   $76.40  
  Purchase #2 $92.42   3.426%   $95.5863   $95.59   $95.60   $95.60  
  Purchase #3 $224.82   3.624%   $232.9675   $232.97   $232.95   $233.00  
  Purchase #4 $32.65   6.264%   $34.6952   $34.70   $34.70   $34.70  
  Purchase #5 $124.94   7.210%   $133.9482   $133.95   $133.95   $133.90  
  Purchase #6 $198.74   10.280%   $219.1705   $219.17   $219.15   $219.20  
  Purchase #7 $52.55   7.494%   $56.4881   $56.49   $56.50   $56.50  
  7 purchase totals = $795.51       $849.3007   $849.31   $849.30   $849.30