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	$110.56	11.384%	$123.1462	$123.15	$123.15	$123.10
Purchase #2	$215.68	10.774%	$238.9174	$238.92	$238.90	$238.90
Purchase #3	$55.77	8.818%	$60.6878	$60.69	$60.70	$60.70
Purchase #4	$188.95	8.435%	$204.8879	$204.89	$204.90	$204.90
Purchase #5	$162.82	6.195%	$172.9067	$172.91	$172.90	$172.90
Purchase #6	$180.49	13.484%	$204.8273	$204.83	$204.85	$204.80
Purchase #7	$141.62	12.844%	$159.8097	$159.81	$159.80	$159.80
7 purchase totals =	$1,055.89		$1,165.1830	$1,165.20	$1,165.20	$1,165.10