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 $246.48   6.556%   $262.6392   $262.64   $262.65   $262.60  
  Purchase #2 $45.36   4.458%   $47.3821   $47.38   $47.40   $47.40  
  Purchase #3 $240.84   13.227%   $272.6959   $272.70   $272.70   $272.70  
  Purchase #4 $39.45   5.599%   $41.6588   $41.66   $41.65   $41.70  
  Purchase #5 $186.97   5.658%   $197.5488   $197.55   $197.55   $197.50  
  Purchase #6 $160.55   6.693%   $171.2956   $171.30   $171.30   $171.30  
  Purchase #7 $238.69   7.519%   $256.6371   $256.64   $256.65   $256.60  
  7 purchase totals = $1,158.34       $1,249.8575   $1,249.87   $1,249.90   $1,249.80