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	$80.26	12.352%	$90.1737	$90.17	$90.15	$90.20
Purchase #2	$169.83	12.151%	$190.466	$190.47	$190.45	$190.50
Purchase #3	$142.36	9.722%	$156.2002	$156.20	$156.20	$156.20
Purchase #4	$86.84	11.147%	$96.5201	$96.52	$96.50	$96.50
Purchase #5	$40.46	5.690%	$42.7622	$42.76	$42.75	$42.80
Purchase #6	$222.91	13.775%	$253.6159	$253.62	$253.60	$253.60
Purchase #7	$220.73	4.423%	$230.4929	$230.49	$230.50	$230.50
7 purchase totals =	$963.39		$1,060.2310	$1,060.23	$1,060.15	$1,060.30