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 $174.79   6.783%   $186.646   $186.65   $186.65   $186.60  
  Purchase #2 $61.63   10.417%   $68.05   $68.05   $68.05   $68.10  
  Purchase #3 $210.48   5.448%   $221.947   $221.95   $221.95   $221.90  
  Purchase #4 $178.28   5.635%   $188.3261   $188.33   $188.35   $188.30  
  Purchase #5 $214.84   7.563%   $231.0883   $231.09   $231.10   $231.10  
  Purchase #6 $56.43   6.538%   $60.1194   $60.12   $60.10   $60.10  
  Purchase #7 $172.85   7.251%   $185.3834   $185.38   $185.40   $185.40  
  7 purchase totals = $1,069.30       $1,141.5602   $1,141.57   $1,141.60   $1,141.50