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 $208.90   13.347%   $236.7819   $236.78   $236.80   $236.80  
  Purchase #2 $143.47   9.436%   $157.0078   $157.01   $157.00   $157.00  
  Purchase #3 $136.59   6.164%   $145.0094   $145.01   $145.00   $145.00  
  Purchase #4 $231.79   3.770%   $240.5285   $240.53   $240.55   $240.50  
  Purchase #5 $194.93   9.560%   $213.5653   $213.57   $213.55   $213.60  
  Purchase #6 $68.81   6.472%   $73.2634   $73.26   $73.25   $73.30  
  Purchase #7 $174.72   3.324%   $180.5277   $180.53   $180.55   $180.50  
  7 purchase totals = $1,159.21       $1,246.6840   $1,246.69   $1,246.70   $1,246.70