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 $60.33   7.233%   $64.6937   $64.69   $64.70   $64.70  
  Purchase #2 $5.71   13.408%   $6.4756   $6.48   $6.50   $6.50  
  Purchase #3 $82.55   11.318%   $91.893   $91.89   $91.90   $91.90  
  Purchase #4 $51.55   4.613%   $53.928   $53.93   $53.95   $53.90  
  Purchase #5 $211.77   7.764%   $228.2118   $228.21   $228.20   $228.20  
  Purchase #6 $245.79   9.107%   $268.1741   $268.17   $268.15   $268.20  
  Purchase #7 $196.38   6.680%   $209.4982   $209.50   $209.50   $209.50  
  7 purchase totals = $854.08       $922.8744   $922.87   $922.90   $922.90