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 $242.45   10.122%   $266.9908   $266.99   $267.00   $267.00  
  Purchase #2 $245.37   13.568%   $278.6618   $278.66   $278.65   $278.70  
  Purchase #3 $59.35   13.482%   $67.3516   $67.35   $67.35   $67.40  
  Purchase #4 $157.76   3.533%   $163.3337   $163.33   $163.35   $163.30  
  Purchase #5 $149.34   6.427%   $158.9381   $158.94   $158.95   $158.90  
  Purchase #6 $163.93   4.608%   $171.4839   $171.48   $171.50   $171.50  
  Purchase #7 $168.45   6.557%   $179.4953   $179.50   $179.50   $179.50  
  7 purchase totals = $1,186.65       $1,286.2552   $1,286.25   $1,286.30   $1,286.30