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	$233.77	8.685%	$254.0729	$254.07	$254.05	$254.10
Purchase #2	$155.69	9.863%	$171.0457	$171.05	$171.05	$171.00
Purchase #3	$127.96	11.628%	$142.8392	$142.84	$142.85	$142.80
Purchase #4	$55.84	7.352%	$59.9454	$59.95	$59.95	$59.90
Purchase #5	$120.85	6.735%	$128.9892	$128.99	$129.00	$129.00
Purchase #6	$182.95	7.294%	$196.2944	$196.29	$196.30	$196.30
Purchase #7	$19.34	8.259%	$20.9373	$20.94	$20.95	$20.90
7 purchase totals =	$896.40		$974.1241	$974.13	$974.15	$974.00