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	$170.76	8.673%	$185.57	$185.57	$185.55	$185.60
Purchase #2	$50.66	7.392%	$54.4048	$54.40	$54.40	$54.40
Purchase #3	$96.76	11.497%	$107.8845	$107.88	$107.90	$107.90
Purchase #4	$243.81	10.401%	$269.1687	$269.17	$269.15	$269.20
Purchase #5	$27.90	4.544%	$29.1678	$29.17	$29.15	$29.20
Purchase #6	$193.81	3.245%	$200.0991	$200.10	$200.10	$200.10
Purchase #7	$137.84	4.741%	$144.375	$144.38	$144.40	$144.40
7 purchase totals =	$921.54		$990.6699	$990.67	$990.65	$990.80