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	$137.66	13.581%	$156.3556	$156.36	$156.35	$156.40
Purchase #2	$151.88	8.869%	$165.3502	$165.35	$165.35	$165.40
Purchase #3	$18.73	3.782%	$19.4384	$19.44	$19.45	$19.40
Purchase #4	$196.77	4.184%	$205.0029	$205.00	$205.00	$205.00
Purchase #5	$135.78	8.160%	$146.8596	$146.86	$146.85	$146.90
Purchase #6	$20.49	3.849%	$21.2787	$21.28	$21.30	$21.30
Purchase #7	$105.27	5.268%	$110.8156	$110.82	$110.80	$110.80
7 purchase totals =	$766.58		$825.1010	$825.11	$825.10	$825.20