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	$83.50	9.197%	$91.1795	$91.18	$91.20	$91.20
Purchase #2	$145.82	13.666%	$165.7478	$165.75	$165.75	$165.70
Purchase #3	$28.30	10.688%	$31.3247	$31.32	$31.30	$31.30
Purchase #4	$78.93	11.788%	$88.2343	$88.23	$88.25	$88.20
Purchase #5	$151.49	10.105%	$166.7981	$166.80	$166.80	$166.80
Purchase #6	$99.56	12.220%	$111.7262	$111.73	$111.75	$111.70
Purchase #7	$103.69	13.655%	$117.8489	$117.85	$117.85	$117.80
7 purchase totals =	$691.29		$772.8595	$772.86	$772.90	$772.70