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	$200.78	4.327%	$209.4678	$209.47	$209.45	$209.50
Purchase #2	$97.76	8.266%	$105.8408	$105.84	$105.85	$105.80
Purchase #3	$240.83	13.715%	$273.8598	$273.86	$273.85	$273.90
Purchase #4	$97.38	10.782%	$107.8795	$107.88	$107.90	$107.90
Purchase #5	$47.92	10.628%	$53.0129	$53.01	$53.00	$53.00
Purchase #6	$131.38	7.165%	$140.7934	$140.79	$140.80	$140.80
Purchase #7	$38.25	10.716%	$42.3489	$42.35	$42.35	$42.30
7 purchase totals =	$854.30		$933.2031	$933.20	$933.20	$933.20