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	$51.46	7.302%	$55.2176	$55.22	$55.20	$55.20
Purchase #2	$214.62	8.640%	$233.1632	$233.16	$233.15	$233.20
Purchase #3	$189.32	6.425%	$201.4838	$201.48	$201.50	$201.50
Purchase #4	$101.51	13.177%	$114.886	$114.89	$114.90	$114.90
Purchase #5	$89.80	7.639%	$96.6598	$96.66	$96.65	$96.70
Purchase #6	$82.58	3.635%	$85.5818	$85.58	$85.60	$85.60
Purchase #7	$100.79	4.320%	$105.1441	$105.14	$105.15	$105.10
7 purchase totals =	$830.08		$892.1363	$892.13	$892.15	$892.20