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	$239.71	7.582%	$257.8848	$257.88	$257.90	$257.90
Purchase #2	$117.62	9.402%	$128.6786	$128.68	$128.70	$128.70
Purchase #3	$48.30	10.199%	$53.2261	$53.23	$53.25	$53.20
Purchase #4	$123.56	5.567%	$130.4386	$130.44	$130.45	$130.40
Purchase #5	$180.68	5.152%	$189.9886	$189.99	$190.00	$190.00
Purchase #6	$17.72	13.309%	$20.0784	$20.08	$20.10	$20.10
Purchase #7	$197.51	12.818%	$222.8268	$222.83	$222.85	$222.80
7 purchase totals =	$925.10		$1,003.1219	$1,003.13	$1,003.25	$1,003.10