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 $183.40   11.371%   $204.2544   $204.25   $204.25   $204.30  
  Purchase #2 $139.63   10.145%   $153.7955   $153.80   $153.80   $153.80  
  Purchase #3 $132.58   5.803%   $140.2736   $140.27   $140.25   $140.30  
  Purchase #4 $222.40   8.482%   $241.264   $241.26   $241.25   $241.30  
  Purchase #5 $162.83   6.832%   $173.9545   $173.95   $173.95   $174.00  
  Purchase #6 $76.84   11.813%   $85.9171   $85.92   $85.90   $85.90  
  Purchase #7 $161.96   8.695%   $176.0424   $176.04   $176.05   $176.00  
  7 purchase totals = $1,079.64       $1,175.5015   $1,175.49   $1,175.45   $1,175.60