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	$238.31	7.274%	$255.6447	$255.64	$255.65	$255.60
Purchase #2	$91.65	8.831%	$99.7436	$99.74	$99.75	$99.70
Purchase #3	$5.70	13.598%	$6.4751	$6.48	$6.50	$6.50
Purchase #4	$78.45	4.326%	$81.8437	$81.84	$81.85	$81.80
Purchase #5	$113.49	8.529%	$123.1696	$123.17	$123.15	$123.20
Purchase #6	$130.44	8.124%	$141.0369	$141.04	$141.05	$141.00
Purchase #7	$189.69	5.370%	$199.8764	$199.88	$199.90	$199.90
7 purchase totals =	$847.73		$907.7900	$907.79	$907.85	$907.70