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	$33.78	5.231%	$35.547	$35.55	$35.55	$35.50
Purchase #2	$110.94	13.834%	$126.2874	$126.29	$126.30	$126.30
Purchase #3	$53.71	7.482%	$57.7286	$57.73	$57.75	$57.70
Purchase #4	$82.73	9.779%	$90.8202	$90.82	$90.80	$90.80
Purchase #5	$162.25	7.331%	$174.1445	$174.14	$174.15	$174.10
Purchase #6	$115.94	12.601%	$130.5496	$130.55	$130.55	$130.50
Purchase #7	$105.66	8.787%	$114.9443	$114.94	$114.95	$114.90
7 purchase totals =	$665.01		$730.0216	$730.02	$730.05	$729.80