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	$128.69	13.253%	$145.7453	$145.75	$145.75	$145.70
Purchase #2	$125.55	11.595%	$140.1075	$140.11	$140.10	$140.10
Purchase #3	$92.79	10.867%	$102.8735	$102.87	$102.85	$102.90
Purchase #4	$158.71	4.573%	$165.9678	$165.97	$165.95	$166.00
Purchase #5	$101.46	9.551%	$111.1504	$111.15	$111.15	$111.20
Purchase #6	$129.70	9.712%	$142.2965	$142.30	$142.30	$142.30
Purchase #7	$177.62	4.257%	$185.1813	$185.18	$185.20	$185.20
7 purchase totals =	$914.52		$993.3223	$993.33	$993.30	$993.40