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 $242.65   8.201%   $262.5497   $262.55   $262.55   $262.50  
  Purchase #2 $6.83   6.579%   $7.2793   $7.28   $7.30   $7.30  
  Purchase #3 $186.32   7.842%   $200.9312   $200.93   $200.95   $200.90  
  Purchase #4 $207.80   11.245%   $231.1671   $231.17   $231.15   $231.20  
  Purchase #5 $166.49   12.530%   $187.3512   $187.35   $187.35   $187.40  
  Purchase #6 $250.74   12.702%   $282.589   $282.59   $282.60   $282.60  
  Purchase #7 $245.46   12.116%   $275.1999   $275.20   $275.20   $275.20  
  7 purchase totals = $1,306.29       $1,447.0674   $1,447.07   $1,447.10   $1,447.10