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	$115.94	8.561%	$125.8656	$125.87	$125.85	$125.90
Purchase #2	$35.93	10.724%	$39.7831	$39.78	$39.80	$39.80
Purchase #3	$232.70	4.833%	$243.9464	$243.95	$243.95	$243.90
Purchase #4	$154.95	11.155%	$172.2347	$172.23	$172.25	$172.20
Purchase #5	$81.28	10.117%	$89.5031	$89.50	$89.50	$89.50
Purchase #6	$196.54	12.205%	$220.5277	$220.53	$220.55	$220.50
Purchase #7	$83.77	6.405%	$89.1355	$89.14	$89.15	$89.10
7 purchase totals =	$901.11		$980.9961	$981.00	$981.05	$980.90