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	$122.59	3.743%	$127.1785	$127.18	$127.20	$127.20
Purchase #2	$188.70	7.831%	$203.4771	$203.48	$203.50	$203.50
Purchase #3	$89.37	11.314%	$99.4813	$99.48	$99.50	$99.50
Purchase #4	$50.90	9.665%	$55.8195	$55.82	$55.80	$55.80
Purchase #5	$73.45	9.829%	$80.6694	$80.67	$80.65	$80.70
Purchase #6	$26.62	10.458%	$29.4039	$29.40	$29.40	$29.40
Purchase #7	$231.98	3.132%	$239.2456	$239.25	$239.25	$239.20
7 purchase totals =	$783.61		$835.2753	$835.28	$835.30	$835.30