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	$21.46	13.668%	$24.3932	$24.39	$24.40	$24.40
Purchase #2	$200.54	7.655%	$215.8913	$215.89	$215.90	$215.90
Purchase #3	$91.62	5.284%	$96.4612	$96.46	$96.45	$96.50
Purchase #4	$42.38	8.794%	$46.1069	$46.11	$46.10	$46.10
Purchase #5	$61.31	6.260%	$65.148	$65.15	$65.15	$65.10
Purchase #6	$9.96	4.345%	$10.3928	$10.39	$10.40	$10.40
Purchase #7	$63.55	13.788%	$72.3123	$72.31	$72.30	$72.30
7 purchase totals =	$490.82		$530.7057	$530.70	$530.70	$530.70