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	$65.70	6.743%	$70.1302	$70.13	$70.15	$70.10
Purchase #2	$134.46	7.769%	$144.9062	$144.91	$144.90	$144.90
Purchase #3	$110.38	5.627%	$116.5911	$116.59	$116.60	$116.60
Purchase #4	$133.95	11.163%	$148.9028	$148.90	$148.90	$148.90
Purchase #5	$6.65	12.806%	$7.5016	$7.50	$7.50	$7.50
Purchase #6	$75.70	8.607%	$82.2155	$82.22	$82.20	$82.20
Purchase #7	$205.76	6.331%	$218.7867	$218.79	$218.80	$218.80
7 purchase totals =	$732.60		$789.0341	$789.04	$789.05	$789.00