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 $241.39   13.514%   $274.0114   $274.01   $274.00   $274.00  
  Purchase #2 $224.37   3.205%   $231.5611   $231.56   $231.55   $231.60  
  Purchase #3 $167.70   13.567%   $190.4519   $190.45   $190.45   $190.50  
  Purchase #4 $140.58   11.283%   $156.4416   $156.44   $156.45   $156.40  
  Purchase #5 $142.71   10.811%   $158.1384   $158.14   $158.15   $158.10  
  Purchase #6 $230.94   10.223%   $254.549   $254.55   $254.55   $254.50  
  Purchase #7 $24.59   8.677%   $26.7237   $26.72   $26.70   $26.70  
  7 purchase totals = $1,172.28       $1,291.8771   $1,291.87   $1,291.85   $1,291.80