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	$74.58	3.655%	$77.3059	$77.31	$77.30	$77.30
Purchase #2	$108.92	3.767%	$113.023	$113.02	$113.00	$113.00
Purchase #3	$43.64	12.530%	$49.1081	$49.11	$49.10	$49.10
Purchase #4	$209.57	10.476%	$231.5246	$231.52	$231.50	$231.50
Purchase #5	$13.76	11.289%	$15.3134	$15.31	$15.30	$15.30
Purchase #6	$210.69	13.270%	$238.6486	$238.65	$238.65	$238.60
Purchase #7	$57.54	3.610%	$59.6172	$59.62	$59.60	$59.60
7 purchase totals =	$718.70		$784.5408	$784.54	$784.45	$784.40