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 $240.33   9.325%   $262.7408   $262.74   $262.75   $262.70  
  Purchase #2 $172.95   13.699%   $196.6424   $196.64   $196.65   $196.60  
  Purchase #3 $176.47   11.553%   $196.8576   $196.86   $196.85   $196.90  
  Purchase #4 $189.77   5.222%   $199.6798   $199.68   $199.70   $199.70  
  Purchase #5 $146.71   9.471%   $160.6049   $160.60   $160.60   $160.60  
  Purchase #6 $128.90   5.356%   $135.8039   $135.80   $135.80   $135.80  
  Purchase #7 $69.64   6.177%   $73.9417   $73.94   $73.95   $73.90  
  7 purchase totals = $1,124.77       $1,226.2711   $1,226.26   $1,226.30   $1,226.20