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 $238.93   3.175%   $246.516   $246.52   $246.50   $246.50  
  Purchase #2 $131.46   8.162%   $142.1898   $142.19   $142.20   $142.20  
  Purchase #3 $146.37   7.827%   $157.8264   $157.83   $157.85   $157.80  
  Purchase #4 $219.70   4.863%   $230.384   $230.38   $230.40   $230.40  
  Purchase #5 $121.58   11.495%   $135.5556   $135.56   $135.55   $135.60  
  Purchase #6 $209.50   9.136%   $228.6399   $228.64   $228.65   $228.60  
  Purchase #7 $66.47   8.430%   $72.0734   $72.07   $72.05   $72.10  
  7 purchase totals = $1,134.01       $1,213.1851   $1,213.19   $1,213.20   $1,213.20