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	$80.55	11.867%	$90.1089	$90.11	$90.10	$90.10
Purchase #2	$81.83	8.765%	$89.0024	$89.00	$89.00	$89.00
Purchase #3	$143.73	7.838%	$154.9956	$155.00	$155.00	$155.00
Purchase #4	$227.36	9.496%	$248.9501	$248.95	$248.95	$249.00
Purchase #5	$97.56	13.856%	$111.0779	$111.08	$111.10	$111.10
Purchase #6	$192.82	10.410%	$212.8926	$212.89	$212.90	$212.90
Purchase #7	$47.43	10.799%	$52.552	$52.55	$52.55	$52.60
7 purchase totals =	$871.28		$959.5795	$959.58	$959.60	$959.70