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	$242.61	12.826%	$273.7272	$273.73	$273.75	$273.70
Purchase #2	$244.29	4.784%	$255.9768	$255.98	$256.00	$256.00
Purchase #3	$85.90	4.249%	$89.5499	$89.55	$89.55	$89.50
Purchase #4	$53.55	9.682%	$58.7347	$58.73	$58.75	$58.70
Purchase #5	$90.87	12.437%	$102.1715	$102.17	$102.15	$102.20
Purchase #6	$221.93	6.390%	$236.1113	$236.11	$236.10	$236.10
Purchase #7	$131.72	4.509%	$137.6593	$137.66	$137.65	$137.70
7 purchase totals =	$1,070.87		$1,153.9307	$1,153.93	$1,153.95	$1,153.90