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	$95.35	4.631%	$99.7657	$99.77	$99.75	$99.80
Purchase #2	$85.88	7.609%	$92.4146	$92.41	$92.40	$92.40
Purchase #3	$118.44	4.211%	$123.4275	$123.43	$123.45	$123.40
Purchase #4	$52.66	8.350%	$57.0571	$57.06	$57.05	$57.10
Purchase #5	$86.87	3.470%	$89.8844	$89.88	$89.90	$89.90
Purchase #6	$34.84	6.866%	$37.2321	$37.23	$37.25	$37.20
Purchase #7	$141.26	6.412%	$150.3176	$150.32	$150.30	$150.30
7 purchase totals =	$615.30		$650.0990	$650.10	$650.10	$650.10