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 $195.55   3.793%   $202.9672   $202.97   $202.95   $203.00  
  Purchase #2 $138.71   10.112%   $152.7364   $152.74   $152.75   $152.70  
  Purchase #3 $205.37   4.385%   $214.3755   $214.38   $214.40   $214.40  
  Purchase #4 $6.53   13.804%   $7.4314   $7.43   $7.45   $7.40  
  Purchase #5 $163.31   13.655%   $185.61   $185.61   $185.60   $185.60  
  Purchase #6 $241.74   8.686%   $262.7375   $262.74   $262.75   $262.70  
  Purchase #7 $218.25   10.463%   $241.0855   $241.09   $241.10   $241.10  
  7 purchase totals = $1,169.46       $1,266.9435   $1,266.96   $1,267.00   $1,266.90