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	$25.46	13.844%	$28.9847	$28.98	$29.00	$29.00
Purchase #2	$93.93	12.126%	$105.32	$105.32	$105.30	$105.30
Purchase #3	$120.38	6.148%	$127.781	$127.78	$127.80	$127.80
Purchase #4	$210.90	11.546%	$235.2505	$235.25	$235.25	$235.30
Purchase #5	$34.36	10.387%	$37.929	$37.93	$37.95	$37.90
Purchase #6	$129.39	4.464%	$135.166	$135.17	$135.15	$135.20
Purchase #7	$48.34	10.435%	$53.3843	$53.38	$53.40	$53.40
7 purchase totals =	$662.76		$723.8155	$723.81	$723.85	$723.90