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 $92.87   9.782%   $101.9545   $101.95   $101.95   $102.00  
  Purchase #2 $51.72   13.315%   $58.6065   $58.61   $58.60   $58.60  
  Purchase #3 $246.95   13.799%   $281.0266   $281.03   $281.05   $281.00  
  Purchase #4 $229.45   8.174%   $248.2052   $248.21   $248.20   $248.20  
  Purchase #5 $119.90   7.473%   $128.8601   $128.86   $128.85   $128.90  
  Purchase #6 $101.47   6.616%   $108.1833   $108.18   $108.20   $108.20  
  Purchase #7 $111.81   13.825%   $127.2677   $127.27   $127.25   $127.30  
  7 purchase totals = $954.17       $1,054.1039   $1,054.11   $1,054.10   $1,054.20