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	$104.53	6.102%	$110.9084	$110.91	$110.90	$110.90
Purchase #2	$180.98	8.725%	$196.7705	$196.77	$196.75	$196.80
Purchase #3	$134.64	12.166%	$151.0203	$151.02	$151.00	$151.00
Purchase #4	$61.63	5.707%	$65.1472	$65.15	$65.15	$65.10
Purchase #5	$191.45	10.104%	$210.7941	$210.79	$210.80	$210.80
Purchase #6	$96.31	4.703%	$100.8395	$100.84	$100.85	$100.80
Purchase #7	$14.38	4.601%	$15.0416	$15.04	$15.05	$15.00
7 purchase totals =	$783.92		$850.5216	$850.52	$850.50	$850.40