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 $227.64   9.860%   $250.0853   $250.09   $250.10   $250.10  
  Purchase #2 $183.36   7.459%   $197.0368   $197.04   $197.05   $197.00  
  Purchase #3 $210.66   6.164%   $223.6451   $223.65   $223.65   $223.60  
  Purchase #4 $65.51   4.855%   $68.6905   $68.69   $68.70   $68.70  
  Purchase #5 $237.25   3.341%   $245.1765   $245.18   $245.20   $245.20  
  Purchase #6 $14.51   9.379%   $15.8709   $15.87   $15.85   $15.90  
  Purchase #7 $122.75   7.206%   $131.5954   $131.60   $131.60   $131.60  
  7 purchase totals = $1,061.68       $1,132.1005   $1,132.12   $1,132.15   $1,132.10