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	$27.81	11.567%	$31.0268	$31.03	$31.05	$31.00
Purchase #2	$157.35	11.554%	$175.5302	$175.53	$175.55	$175.50
Purchase #3	$159.55	9.536%	$174.7647	$174.76	$174.75	$174.80
Purchase #4	$118.29	4.328%	$123.4096	$123.41	$123.40	$123.40
Purchase #5	$110.32	4.204%	$114.9579	$114.96	$114.95	$115.00
Purchase #6	$207.82	7.362%	$223.1197	$223.12	$223.10	$223.10
Purchase #7	$197.50	9.594%	$216.4482	$216.45	$216.45	$216.40
7 purchase totals =	$978.64		$1,059.2571	$1,059.26	$1,059.25	$1,059.20