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 $150.66   7.502%   $161.9625   $161.96   $161.95   $162.00  
  Purchase #2 $94.54   5.194%   $99.4504   $99.45   $99.45   $99.50  
  Purchase #3 $249.61   7.465%   $268.2434   $268.24   $268.25   $268.20  
  Purchase #4 $126.50   6.771%   $135.0653   $135.07   $135.05   $135.10  
  Purchase #5 $202.39   6.348%   $215.2377   $215.24   $215.25   $215.20  
  Purchase #6 $39.41   3.449%   $40.7693   $40.77   $40.75   $40.80  
  Purchase #7 $92.55   6.543%   $98.6055   $98.61   $98.60   $98.60  
  7 purchase totals = $955.66       $1,019.3341   $1,019.34   $1,019.30   $1,019.40