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	$18.75	8.139%	$20.2761	$20.28	$20.30	$20.30
Purchase #2	$98.87	8.356%	$107.1316	$107.13	$107.15	$107.10
Purchase #3	$151.64	9.168%	$165.5424	$165.54	$165.55	$165.50
Purchase #4	$233.72	10.765%	$258.88	$258.88	$258.90	$258.90
Purchase #5	$134.34	3.823%	$139.4758	$139.48	$139.50	$139.50
Purchase #6	$76.93	12.520%	$86.5616	$86.56	$86.55	$86.60
Purchase #7	$129.56	13.674%	$147.276	$147.28	$147.30	$147.30
7 purchase totals =	$843.81		$925.1435	$925.15	$925.25	$925.20