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 $191.99   6.284%   $204.0547   $204.05   $204.05   $204.10  
  Purchase #2 $226.87   11.253%   $252.3997   $252.40   $252.40   $252.40  
  Purchase #3 $65.69   8.867%   $71.5147   $71.51   $71.50   $71.50  
  Purchase #4 $220.80   12.204%   $247.7464   $247.75   $247.75   $247.70  
  Purchase #5 $64.74   11.852%   $72.413   $72.41   $72.40   $72.40  
  Purchase #6 $144.89   6.149%   $153.7993   $153.80   $153.80   $153.80  
  Purchase #7 $178.38   10.204%   $196.5819   $196.58   $196.60   $196.60  
  7 purchase totals = $1,093.36       $1,198.5097   $1,198.50   $1,198.50   $1,198.50