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	$69.67	12.407%	$78.314	$78.31	$78.30	$78.30
Purchase #2	$173.69	3.522%	$179.8074	$179.81	$179.80	$179.80
Purchase #3	$50.54	9.196%	$55.1877	$55.19	$55.20	$55.20
Purchase #4	$38.89	3.542%	$40.2675	$40.27	$40.25	$40.30
Purchase #5	$120.46	5.513%	$127.101	$127.10	$127.10	$127.10
Purchase #6	$98.34	9.618%	$107.7983	$107.80	$107.80	$107.80
Purchase #7	$68.58	12.386%	$77.0743	$77.07	$77.05	$77.10
7 purchase totals =	$620.17		$665.5502	$665.55	$665.50	$665.60