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	$64.57	13.258%	$73.1307	$73.13	$73.15	$73.10
Purchase #2	$145.27	9.196%	$158.629	$158.63	$158.65	$158.60
Purchase #3	$38.81	4.844%	$40.69	$40.69	$40.70	$40.70
Purchase #4	$196.98	4.639%	$206.1179	$206.12	$206.10	$206.10
Purchase #5	$53.90	4.231%	$56.1805	$56.18	$56.20	$56.20
Purchase #6	$19.50	5.803%	$20.6316	$20.63	$20.65	$20.60
Purchase #7	$175.52	8.730%	$190.8429	$190.84	$190.85	$190.80
7 purchase totals =	$694.55		$746.2226	$746.22	$746.30	$746.10