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	$85.80	5.794%	$90.7713	$90.77	$90.75	$90.80
Purchase #2	$135.51	13.766%	$154.1643	$154.16	$154.15	$154.20
Purchase #3	$235.57	5.652%	$248.8844	$248.88	$248.90	$248.90
Purchase #4	$144.42	3.674%	$149.726	$149.73	$149.75	$149.70
Purchase #5	$181.28	8.550%	$196.7794	$196.78	$196.80	$196.80
Purchase #6	$193.29	6.609%	$206.0645	$206.06	$206.05	$206.10
Purchase #7	$231.84	9.771%	$254.4931	$254.49	$254.50	$254.50
7 purchase totals =	$1,207.71		$1,300.8830	$1,300.87	$1,300.90	$1,301.00