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	$85.59	7.644%	$92.1325	$92.13	$92.15	$92.10
Purchase #2	$44.33	9.255%	$48.4327	$48.43	$48.45	$48.40
Purchase #3	$76.40	5.116%	$80.3086	$80.31	$80.30	$80.30
Purchase #4	$132.42	6.623%	$141.1902	$141.19	$141.20	$141.20
Purchase #5	$243.77	10.274%	$268.8149	$268.81	$268.80	$268.80
Purchase #6	$165.30	13.448%	$187.5295	$187.53	$187.55	$187.50
Purchase #7	$18.50	9.841%	$20.3206	$20.32	$20.30	$20.30
7 purchase totals =	$766.31		$838.7290	$838.72	$838.75	$838.60