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	$100.56	10.694%	$111.3139	$111.31	$111.30	$111.30
Purchase #2	$112.57	5.257%	$118.4878	$118.49	$118.50	$118.50
Purchase #3	$143.56	9.567%	$157.2944	$157.29	$157.30	$157.30
Purchase #4	$55.34	4.370%	$57.7584	$57.76	$57.75	$57.80
Purchase #5	$113.46	4.292%	$118.3297	$118.33	$118.35	$118.30
Purchase #6	$82.90	7.298%	$88.95	$88.95	$88.95	$89.00
Purchase #7	$159.28	9.857%	$174.9802	$174.98	$175.00	$175.00
7 purchase totals =	$767.67		$827.1144	$827.11	$827.15	$827.20