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	$107.70	9.809%	$118.2643	$118.26	$118.25	$118.30
Purchase #2	$111.74	6.713%	$119.2411	$119.24	$119.25	$119.20
Purchase #3	$54.25	4.873%	$56.8936	$56.89	$56.90	$56.90
Purchase #4	$94.37	11.641%	$105.3556	$105.36	$105.35	$105.40
Purchase #5	$28.65	9.250%	$31.3001	$31.30	$31.30	$31.30
Purchase #6	$133.48	12.731%	$150.4733	$150.47	$150.45	$150.50
Purchase #7	$235.54	7.852%	$254.0346	$254.03	$254.05	$254.00
7 purchase totals =	$765.73		$835.5626	$835.55	$835.55	$835.60