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	$117.52	4.339%	$122.6192	$122.62	$122.60	$122.60
Purchase #2	$78.65	5.700%	$83.1331	$83.13	$83.15	$83.10
Purchase #3	$62.74	7.289%	$67.3131	$67.31	$67.30	$67.30
Purchase #4	$63.55	5.464%	$67.0224	$67.02	$67.00	$67.00
Purchase #5	$28.48	5.110%	$29.9353	$29.94	$29.95	$29.90
Purchase #6	$90.41	6.734%	$96.4982	$96.50	$96.50	$96.50
Purchase #7	$80.82	5.559%	$85.3128	$85.31	$85.30	$85.30
7 purchase totals =	$522.17		$551.8341	$551.83	$551.80	$551.70