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	$61.37	4.679%	$64.2415	$64.24	$64.25	$64.20
Purchase #2	$230.83	13.452%	$261.8813	$261.88	$261.90	$261.90
Purchase #3	$26.39	13.478%	$29.9468	$29.95	$29.95	$29.90
Purchase #4	$58.94	13.441%	$66.8621	$66.86	$66.85	$66.90
Purchase #5	$203.67	12.511%	$229.1512	$229.15	$229.15	$229.20
Purchase #6	$71.54	8.404%	$77.5522	$77.55	$77.55	$77.60
Purchase #7	$80.29	6.342%	$85.382	$85.38	$85.40	$85.40
7 purchase totals =	$733.03		$815.0171	$815.01	$815.05	$815.10