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 $213.49   13.413%   $242.1254   $242.13   $242.15   $242.10  
  Purchase #2 $134.57   12.587%   $151.5083   $151.51   $151.50   $151.50  
  Purchase #3 $187.75   13.123%   $212.3884   $212.39   $212.40   $212.40  
  Purchase #4 $106.66   3.532%   $110.4272   $110.43   $110.45   $110.40  
  Purchase #5 $41.82   8.648%   $45.4366   $45.44   $45.45   $45.40  
  Purchase #6 $233.88   6.677%   $249.4962   $249.50   $249.50   $249.50  
  Purchase #7 $191.59   7.135%   $205.2599   $205.26   $205.25   $205.30  
  7 purchase totals = $1,109.76       $1,216.6420   $1,216.66   $1,216.70   $1,216.60