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	$80.50	3.201%	$83.0768	$83.08	$83.10	$83.10
Purchase #2	$18.78	11.800%	$20.996	$21.00	$21.00	$21.00
Purchase #3	$118.96	8.235%	$128.7564	$128.76	$128.75	$128.80
Purchase #4	$134.33	7.727%	$144.7097	$144.71	$144.70	$144.70
Purchase #5	$40.91	3.669%	$42.411	$42.41	$42.40	$42.40
Purchase #6	$25.93	4.769%	$27.1666	$27.17	$27.15	$27.20
Purchase #7	$53.92	6.731%	$57.5494	$57.55	$57.55	$57.50
7 purchase totals =	$473.33		$504.6659	$504.68	$504.65	$504.70