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 $47.49   3.418%   $49.1132   $49.11   $49.10   $49.10  
  Purchase #2 $249.31   5.191%   $262.2517   $262.25   $262.25   $262.30  
  Purchase #3 $131.63   12.113%   $147.5743   $147.57   $147.55   $147.60  
  Purchase #4 $187.71   12.201%   $210.6125   $210.61   $210.60   $210.60  
  Purchase #5 $54.57   10.264%   $60.1711   $60.17   $60.15   $60.20  
  Purchase #6 $120.91   12.305%   $135.788   $135.79   $135.80   $135.80  
  Purchase #7 $91.34   10.472%   $100.9051   $100.91   $100.90   $100.90  
  7 purchase totals = $882.96       $966.4159   $966.41   $966.35   $966.50