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 $119.25   6.294%   $126.7556   $126.76   $126.75   $126.80  
  Purchase #2 $126.53   10.589%   $139.9283   $139.93   $139.95   $139.90  
  Purchase #3 $134.40   11.124%   $149.3507   $149.35   $149.35   $149.40  
  Purchase #4 $14.55   10.681%   $16.1041   $16.10   $16.10   $16.10  
  Purchase #5 $7.63   13.197%   $8.6369   $8.64   $8.65   $8.60  
  Purchase #6 $22.37   12.268%   $25.1144   $25.11   $25.10   $25.10  
  Purchase #7 $26.30   6.498%   $28.009   $28.01   $28.00   $28.00  
  7 purchase totals = $451.03       $493.8990   $493.90   $493.90   $493.90