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	$89.67	10.388%	$98.9849	$98.98	$99.00	$99.00
Purchase #2	$131.42	8.344%	$142.3857	$142.39	$142.40	$142.40
Purchase #3	$98.36	11.595%	$109.7648	$109.76	$109.75	$109.80
Purchase #4	$225.43	3.367%	$233.0202	$233.02	$233.00	$233.00
Purchase #5	$204.60	9.356%	$223.7424	$223.74	$223.75	$223.70
Purchase #6	$247.77	6.616%	$264.1625	$264.16	$264.15	$264.20
Purchase #7	$208.83	3.537%	$216.2163	$216.22	$216.20	$216.20
7 purchase totals =	$1,206.08		$1,288.2768	$1,288.27	$1,288.25	$1,288.30