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 $67.44   9.697%   $73.9797   $73.98   $74.00   $74.00  
  Purchase #2 $240.39   6.150%   $255.174   $255.17   $255.15   $255.20  
  Purchase #3 $73.94   6.443%   $78.704   $78.70   $78.70   $78.70  
  Purchase #4 $186.53   12.422%   $209.7008   $209.70   $209.70   $209.70  
  Purchase #5 $239.83   6.779%   $256.0881   $256.09   $256.10   $256.10  
  Purchase #6 $131.91   13.421%   $149.6136   $149.61   $149.60   $149.60  
  Purchase #7 $192.71   8.484%   $209.0595   $209.06   $209.05   $209.10  
  7 purchase totals = $1,132.75       $1,232.3197   $1,232.31   $1,232.30   $1,232.40