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 $241.87   8.557%   $262.5668   $262.57   $262.55   $262.60  
  Purchase #2 $230.52   8.230%   $249.4918   $249.49   $249.50   $249.50  
  Purchase #3 $34.35   5.822%   $36.3499   $36.35   $36.35   $36.30  
  Purchase #4 $65.85   11.637%   $73.513   $73.51   $73.50   $73.50  
  Purchase #5 $66.33   9.601%   $72.6983   $72.70   $72.70   $72.70  
  Purchase #6 $46.98   5.870%   $49.7377   $49.74   $49.75   $49.70  
  Purchase #7 $158.26   3.588%   $163.9384   $163.94   $163.95   $163.90  
  7 purchase totals = $844.16       $908.2959   $908.30   $908.30   $908.20