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 $119.51   4.144%   $124.4625   $124.46   $124.45   $124.50  
  Purchase #2 $161.94   3.155%   $167.0492   $167.05   $167.05   $167.00  
  Purchase #3 $142.91   4.497%   $149.3367   $149.34   $149.35   $149.30  
  Purchase #4 $158.88   7.858%   $171.3648   $171.36   $171.35   $171.40  
  Purchase #5 $126.63   5.476%   $133.5643   $133.56   $133.55   $133.60  
  Purchase #6 $14.97   12.845%   $16.8929   $16.89   $16.90   $16.90  
  Purchase #7 $245.54   5.782%   $259.7371   $259.74   $259.75   $259.70  
  7 purchase totals = $970.38       $1,022.4075   $1,022.40   $1,022.40   $1,022.40