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 $244.68   8.712%   $265.9965   $266.00   $266.00   $266.00  
  Purchase #2 $173.84   3.449%   $179.8357   $179.84   $179.85   $179.80  
  Purchase #3 $205.60   7.815%   $221.6676   $221.67   $221.65   $221.70  
  Purchase #4 $223.58   9.202%   $244.1538   $244.15   $244.15   $244.20  
  Purchase #5 $59.61   4.455%   $62.2656   $62.27   $62.25   $62.30  
  Purchase #6 $239.75   9.414%   $262.3201   $262.32   $262.30   $262.30  
  Purchase #7 $42.89   8.109%   $46.368   $46.37   $46.35   $46.40  
  7 purchase totals = $1,189.95       $1,282.6073   $1,282.62   $1,282.55   $1,282.70