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 $184.54   5.797%   $195.2378   $195.24   $195.25   $195.20  
  Purchase #2 $74.78   10.611%   $82.7149   $82.71   $82.70   $82.70  
  Purchase #3 $128.95   10.335%   $142.277   $142.28   $142.30   $142.30  
  Purchase #4 $174.54   6.814%   $186.4332   $186.43   $186.45   $186.40  
  Purchase #5 $107.27   7.526%   $115.3431   $115.34   $115.35   $115.30  
  Purchase #6 $89.59   10.432%   $98.936   $98.94   $98.95   $98.90  
  Purchase #7 $57.63   13.478%   $65.3974   $65.40   $65.40   $65.40  
  7 purchase totals = $817.30       $886.3394   $886.34   $886.40   $886.20