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	$223.52	13.243%	$253.1208	$253.12	$253.10	$253.10
Purchase #2	$217.89	5.489%	$229.85	$229.85	$229.85	$229.90
Purchase #3	$197.88	10.102%	$217.8698	$217.87	$217.85	$217.90
Purchase #4	$110.59	4.650%	$115.7324	$115.73	$115.75	$115.70
Purchase #5	$120.71	5.526%	$127.3804	$127.38	$127.40	$127.40
Purchase #6	$97.73	8.416%	$105.955	$105.96	$105.95	$106.00
Purchase #7	$157.69	8.750%	$171.4879	$171.49	$171.50	$171.50
7 purchase totals =	$1,126.01		$1,221.3963	$1,221.40	$1,221.40	$1,221.50