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	$243.44	6.536%	$259.3512	$259.35	$259.35	$259.40
Purchase #2	$126.49	3.306%	$130.6718	$130.67	$130.65	$130.70
Purchase #3	$85.52	10.428%	$94.438	$94.44	$94.45	$94.40
Purchase #4	$72.52	11.779%	$81.0621	$81.06	$81.05	$81.10
Purchase #5	$82.88	7.868%	$89.401	$89.40	$89.40	$89.40
Purchase #6	$193.65	3.110%	$199.6725	$199.67	$199.65	$199.70
Purchase #7	$159.29	3.850%	$165.4227	$165.42	$165.40	$165.40
7 purchase totals =	$963.79		$1,020.0193	$1,020.01	$1,019.95	$1,020.10