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 $189.28   8.295%   $204.9808   $204.98   $205.00   $205.00  
  Purchase #2 $229.37   5.837%   $242.7583   $242.76   $242.75   $242.80  
  Purchase #3 $211.66   8.680%   $230.0321   $230.03   $230.05   $230.00  
  Purchase #4 $94.27   13.579%   $107.0709   $107.07   $107.05   $107.10  
  Purchase #5 $168.53   3.157%   $173.8505   $173.85   $173.85   $173.90  
  Purchase #6 $233.25   6.188%   $247.6835   $247.68   $247.70   $247.70  
  Purchase #7 $84.47   5.404%   $89.0348   $89.03   $89.05   $89.00  
  7 purchase totals = $1,210.83       $1,295.4109   $1,295.40   $1,295.45   $1,295.50