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 $16.75   5.291%   $17.6362   $17.64   $17.65   $17.60  
  Purchase #2 $105.49   3.694%   $109.3868   $109.39   $109.40   $109.40  
  Purchase #3 $6.35   8.717%   $6.9035   $6.90   $6.90   $6.90  
  Purchase #4 $189.60   8.503%   $205.7217   $205.72   $205.70   $205.70  
  Purchase #5 $239.51   5.426%   $252.5058   $252.51   $252.50   $252.50  
  Purchase #6 $169.82   13.139%   $192.1326   $192.13   $192.15   $192.10  
  Purchase #7 $60.63   10.695%   $67.1144   $67.11   $67.10   $67.10  
  7 purchase totals = $788.15       $851.4010   $851.40   $851.40   $851.30