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	$83.61	7.510%	$89.8891	$89.89	$89.90	$89.90
Purchase #2	$234.95	7.711%	$253.067	$253.07	$253.05	$253.10
Purchase #3	$101.49	12.820%	$114.501	$114.50	$114.50	$114.50
Purchase #4	$197.50	12.283%	$221.7589	$221.76	$221.75	$221.80
Purchase #5	$11.82	9.585%	$12.9529	$12.95	$12.95	$13.00
Purchase #6	$175.87	11.414%	$195.9438	$195.94	$195.95	$195.90
Purchase #7	$170.64	9.196%	$186.3321	$186.33	$186.35	$186.30
7 purchase totals =	$975.88		$1,074.4448	$1,074.44	$1,074.45	$1,074.50