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	$94.72	6.398%	$100.7802	$100.78	$100.80	$100.80
Purchase #2	$111.32	3.809%	$115.5602	$115.56	$115.55	$115.60
Purchase #3	$53.76	6.717%	$57.3711	$57.37	$57.35	$57.40
Purchase #4	$242.88	7.115%	$260.1609	$260.16	$260.15	$260.20
Purchase #5	$29.92	8.306%	$32.4052	$32.41	$32.40	$32.40
Purchase #6	$159.84	5.471%	$168.5848	$168.58	$168.60	$168.60
Purchase #7	$27.61	10.289%	$30.4508	$30.45	$30.45	$30.50
7 purchase totals =	$720.05		$765.3132	$765.31	$765.30	$765.50