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	$136.82	7.653%	$147.2908	$147.29	$147.30	$147.30
Purchase #2	$156.92	4.136%	$163.4102	$163.41	$163.40	$163.40
Purchase #3	$223.50	13.202%	$253.0065	$253.01	$253.00	$253.00
Purchase #4	$111.57	12.704%	$125.7439	$125.74	$125.75	$125.70
Purchase #5	$137.32	13.761%	$156.2166	$156.22	$156.20	$156.20
Purchase #6	$98.71	13.294%	$111.8325	$111.83	$111.85	$111.80
Purchase #7	$142.48	6.448%	$151.6671	$151.67	$151.65	$151.70
7 purchase totals =	$1,007.32		$1,109.1676	$1,109.17	$1,109.15	$1,109.10