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 $10.58   9.528%   $11.5881   $11.59   $11.60   $11.60  
  Purchase #2 $167.84   11.112%   $186.4904   $186.49   $186.50   $186.50  
  Purchase #3 $205.57   7.770%   $221.5428   $221.54   $221.55   $221.50  
  Purchase #4 $230.34   7.400%   $247.3852   $247.39   $247.40   $247.40  
  Purchase #5 $190.61   4.202%   $198.6194   $198.62   $198.60   $198.60  
  Purchase #6 $214.36   8.847%   $233.3244   $233.32   $233.30   $233.30  
  Purchase #7 $50.98   7.862%   $54.988   $54.99   $55.00   $55.00  
  7 purchase totals = $1,070.28       $1,153.9383   $1,153.94   $1,153.95   $1,153.90