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	$37.57	4.620%	$39.3057	$39.31	$39.30	$39.30
Purchase #2	$92.61	6.818%	$98.9241	$98.92	$98.90	$98.90
Purchase #3	$84.96	5.461%	$89.5997	$89.60	$89.60	$89.60
Purchase #4	$164.89	3.857%	$171.2498	$171.25	$171.25	$171.20
Purchase #5	$49.75	3.572%	$51.5271	$51.53	$51.55	$51.50
Purchase #6	$50.98	10.173%	$56.1662	$56.17	$56.15	$56.20
Purchase #7	$62.50	7.758%	$67.3488	$67.35	$67.35	$67.30
7 purchase totals =	$543.26		$574.1214	$574.13	$574.10	$574.00