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	$69.52	12.802%	$78.42	$78.42	$78.40	$78.40
Purchase #2	$105.85	11.638%	$118.1688	$118.17	$118.15	$118.20
Purchase #3	$64.56	5.109%	$67.8584	$67.86	$67.85	$67.90
Purchase #4	$39.41	11.198%	$43.8231	$43.82	$43.80	$43.80
Purchase #5	$209.49	7.766%	$225.759	$225.76	$225.75	$225.80
Purchase #6	$173.51	12.546%	$195.2786	$195.28	$195.30	$195.30
Purchase #7	$87.94	12.682%	$99.0926	$99.09	$99.10	$99.10
7 purchase totals =	$750.28		$828.4005	$828.40	$828.35	$828.50