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	$149.73	10.323%	$165.1866	$165.19	$165.20	$165.20
Purchase #2	$37.41	8.575%	$40.6179	$40.62	$40.60	$40.60
Purchase #3	$127.37	3.312%	$131.5885	$131.59	$131.60	$131.60
Purchase #4	$67.65	8.184%	$73.1865	$73.19	$73.20	$73.20
Purchase #5	$95.82	3.776%	$99.4382	$99.44	$99.45	$99.40
Purchase #6	$97.48	7.801%	$105.0844	$105.08	$105.10	$105.10
Purchase #7	$15.32	13.272%	$17.3533	$17.35	$17.35	$17.40
7 purchase totals =	$590.78		$632.4554	$632.46	$632.50	$632.50