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	$35.77	13.222%	$40.4995	$40.50	$40.50	$40.50
Purchase #2	$199.54	13.345%	$226.1686	$226.17	$226.15	$226.20
Purchase #3	$208.98	6.871%	$223.339	$223.34	$223.35	$223.30
Purchase #4	$58.26	10.295%	$64.2579	$64.26	$64.25	$64.30
Purchase #5	$57.55	9.160%	$62.8216	$62.82	$62.80	$62.80
Purchase #6	$105.33	12.396%	$118.3867	$118.39	$118.40	$118.40
Purchase #7	$40.43	4.828%	$42.382	$42.38	$42.40	$42.40
7 purchase totals =	$705.86		$777.8553	$777.86	$777.85	$777.90