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	$243.83	11.643%	$272.2191	$272.22	$272.20	$272.20
Purchase #2	$29.76	6.602%	$31.7248	$31.72	$31.70	$31.70
Purchase #3	$42.80	13.450%	$48.5566	$48.56	$48.55	$48.60
Purchase #4	$154.28	13.388%	$174.935	$174.94	$174.95	$174.90
Purchase #5	$19.31	9.586%	$21.1611	$21.16	$21.15	$21.20
Purchase #6	$70.27	3.143%	$72.4786	$72.48	$72.50	$72.50
Purchase #7	$232.26	13.588%	$263.8195	$263.82	$263.80	$263.80
7 purchase totals =	$792.51		$884.8947	$884.90	$884.85	$884.90