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 $243.79   7.396%   $261.8207   $261.82   $261.80   $261.80  
  Purchase #2 $215.61   9.642%   $236.3991   $236.40   $236.40   $236.40  
  Purchase #3 $125.47   3.533%   $129.9029   $129.90   $129.90   $129.90  
  Purchase #4 $183.65   5.408%   $193.5818   $193.58   $193.60   $193.60  
  Purchase #5 $184.95   6.860%   $197.6376   $197.64   $197.65   $197.60  
  Purchase #6 $113.70   13.106%   $128.6015   $128.60   $128.60   $128.60  
  Purchase #7 $49.93   10.654%   $55.2495   $55.25   $55.25   $55.20  
  7 purchase totals = $1,117.10       $1,203.1931   $1,203.19   $1,203.20   $1,203.10