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	$245.75	13.478%	$278.8722	$278.87	$278.85	$278.90
Purchase #2	$55.53	10.737%	$61.4923	$61.49	$61.50	$61.50
Purchase #3	$170.38	13.333%	$193.0968	$193.10	$193.10	$193.10
Purchase #4	$96.42	9.423%	$105.5057	$105.51	$105.50	$105.50
Purchase #5	$72.61	13.259%	$82.2374	$82.24	$82.25	$82.20
Purchase #6	$198.47	4.679%	$207.7564	$207.76	$207.75	$207.80
Purchase #7	$68.38	6.801%	$73.0305	$73.03	$73.05	$73.00
7 purchase totals =	$907.54		$1,001.9913	$1,002.00	$1,002.00	$1,002.00