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	$89.50	10.322%	$98.7382	$98.74	$98.75	$98.70
Purchase #2	$83.56	10.532%	$92.3605	$92.36	$92.35	$92.40
Purchase #3	$173.26	10.479%	$191.4159	$191.42	$191.40	$191.40
Purchase #4	$59.57	5.593%	$62.9018	$62.90	$62.90	$62.90
Purchase #5	$16.52	6.169%	$17.5391	$17.54	$17.55	$17.50
Purchase #6	$113.53	12.526%	$127.7508	$127.75	$127.75	$127.80
Purchase #7	$86.91	8.383%	$94.1957	$94.20	$94.20	$94.20
7 purchase totals =	$622.85		$684.9020	$684.91	$684.90	$684.90