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	$115.67	3.862%	$120.1372	$120.14	$120.15	$120.10
Purchase #2	$203.28	9.416%	$222.4208	$222.42	$222.40	$222.40
Purchase #3	$212.92	4.528%	$222.561	$222.56	$222.55	$222.60
Purchase #4	$193.83	3.643%	$200.8912	$200.89	$200.90	$200.90
Purchase #5	$8.49	6.825%	$9.0694	$9.07	$9.05	$9.10
Purchase #6	$38.91	4.749%	$40.7578	$40.76	$40.75	$40.80
Purchase #7	$66.47	7.585%	$71.5117	$71.51	$71.50	$71.50
7 purchase totals =	$839.57		$887.3491	$887.35	$887.30	$887.40