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 $60.59   5.274%   $63.7855   $63.79   $63.80   $63.80  
  Purchase #2 $27.49   9.510%   $30.1043   $30.10   $30.10   $30.10  
  Purchase #3 $199.92   3.227%   $206.3714   $206.37   $206.35   $206.40  
  Purchase #4 $192.69   10.113%   $212.1767   $212.18   $212.20   $212.20  
  Purchase #5 $68.70   8.187%   $74.3245   $74.32   $74.30   $74.30  
  Purchase #6 $161.47   8.782%   $175.6503   $175.65   $175.65   $175.70  
  Purchase #7 $246.60   6.375%   $262.3208   $262.32   $262.30   $262.30  
  7 purchase totals = $957.46       $1,024.7335   $1,024.73   $1,024.70   $1,024.80