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	$181.61	9.172%	$198.2673	$198.27	$198.25	$198.30
Purchase #2	$70.92	12.841%	$80.0268	$80.03	$80.05	$80.00
Purchase #3	$18.43	7.738%	$19.8561	$19.86	$19.85	$19.90
Purchase #4	$33.46	11.457%	$37.2935	$37.29	$37.30	$37.30
Purchase #5	$111.53	8.275%	$120.7591	$120.76	$120.75	$120.80
Purchase #6	$124.35	5.718%	$131.4603	$131.46	$131.45	$131.50
Purchase #7	$58.66	5.225%	$61.725	$61.73	$61.75	$61.70
7 purchase totals =	$598.96		$649.3881	$649.40	$649.40	$649.50