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 $175.97   13.818%   $200.2855   $200.29   $200.30   $200.30  
  Purchase #2 $239.88   4.809%   $251.4158   $251.42   $251.40   $251.40  
  Purchase #3 $206.64   9.820%   $226.932   $226.93   $226.95   $226.90  
  Purchase #4 $49.86   7.731%   $53.7147   $53.71   $53.70   $53.70  
  Purchase #5 $167.43   8.422%   $181.531   $181.53   $181.55   $181.50  
  Purchase #6 $135.99   13.651%   $154.554   $154.55   $154.55   $154.60  
  Purchase #7 $154.88   12.606%   $174.4042   $174.40   $174.40   $174.40  
  7 purchase totals = $1,130.65       $1,242.8372   $1,242.83   $1,242.85   $1,242.80