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	$90.76	9.345%	$99.2415	$99.24	$99.25	$99.20
Purchase #2	$94.35	9.694%	$103.4963	$103.50	$103.50	$103.50
Purchase #3	$248.36	8.750%	$270.0915	$270.09	$270.10	$270.10
Purchase #4	$47.98	6.339%	$51.0215	$51.02	$51.00	$51.00
Purchase #5	$127.26	3.415%	$131.6059	$131.61	$131.60	$131.60
Purchase #6	$26.38	7.672%	$28.4039	$28.40	$28.40	$28.40
Purchase #7	$142.61	5.719%	$150.7659	$150.77	$150.75	$150.80
7 purchase totals =	$777.70		$834.6265	$834.63	$834.60	$834.60