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 $56.43   13.190%   $63.8731   $63.87   $63.85   $63.90  
  Purchase #2 $87.27   9.690%   $95.7265   $95.73   $95.75   $95.70  
  Purchase #3 $174.73   5.283%   $183.961   $183.96   $183.95   $184.00  
  Purchase #4 $190.70   8.220%   $206.3755   $206.38   $206.40   $206.40  
  Purchase #5 $13.83   6.645%   $14.749   $14.75   $14.75   $14.70  
  Purchase #6 $241.54   11.156%   $268.4862   $268.49   $268.50   $268.50  
  Purchase #7 $97.99   11.856%   $109.6077   $109.61   $109.60   $109.60  
  7 purchase totals = $862.49       $942.7790   $942.79   $942.80   $942.80