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 $46.80   10.287%   $51.6143   $51.61   $51.60   $51.60  
  Purchase #2 $214.89   13.475%   $243.8464   $243.85   $243.85   $243.80  
  Purchase #3 $24.92   7.141%   $26.6995   $26.70   $26.70   $26.70  
  Purchase #4 $129.63   8.181%   $140.235   $140.24   $140.25   $140.20  
  Purchase #5 $239.53   4.144%   $249.4561   $249.46   $249.45   $249.50  
  Purchase #6 $128.39   13.196%   $145.3323   $145.33   $145.35   $145.30  
  Purchase #7 $126.86   13.308%   $143.7425   $143.74   $143.75   $143.70  
  7 purchase totals = $911.02       $1,000.9261   $1,000.93   $1,000.95   $1,000.80