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	$11.41	9.501%	$12.4941	$12.49	$12.50	$12.50
Purchase #2	$155.42	8.642%	$168.8514	$168.85	$168.85	$168.90
Purchase #3	$38.62	11.523%	$43.0702	$43.07	$43.05	$43.10
Purchase #4	$16.43	13.740%	$18.6875	$18.69	$18.70	$18.70
Purchase #5	$238.64	4.791%	$250.0732	$250.07	$250.05	$250.10
Purchase #6	$150.88	13.854%	$171.7829	$171.78	$171.80	$171.80
Purchase #7	$123.42	7.753%	$132.9888	$132.99	$133.00	$133.00
7 purchase totals =	$734.82		$797.9481	$797.94	$797.95	$798.10