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	$140.66	9.143%	$153.5205	$153.52	$153.50	$153.50
Purchase #2	$147.36	8.311%	$159.6071	$159.61	$159.60	$159.60
Purchase #3	$140.78	6.699%	$150.2109	$150.21	$150.20	$150.20
Purchase #4	$49.56	11.663%	$55.3402	$55.34	$55.35	$55.30
Purchase #5	$27.94	7.827%	$30.1269	$30.13	$30.15	$30.10
Purchase #6	$35.59	5.154%	$37.4243	$37.42	$37.40	$37.40
Purchase #7	$89.94	12.103%	$100.8254	$100.83	$100.85	$100.80
7 purchase totals =	$631.83		$687.0553	$687.06	$687.05	$686.90