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 $224.97   7.481%   $241.8   $241.80   $241.80   $241.80  
  Purchase #2 $72.53   6.122%   $76.9703   $76.97   $76.95   $77.00  
  Purchase #3 $25.27   9.688%   $27.7182   $27.72   $27.70   $27.70  
  Purchase #4 $151.66   8.235%   $164.1492   $164.15   $164.15   $164.10  
  Purchase #5 $241.91   10.307%   $266.8437   $266.84   $266.85   $266.80  
  Purchase #6 $250.70   10.872%   $277.9561   $277.96   $277.95   $278.00  
  Purchase #7 $170.53   8.343%   $184.7573   $184.76   $184.75   $184.80  
  7 purchase totals = $1,137.57       $1,240.1948   $1,240.20   $1,240.15   $1,240.20