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	$230.57	6.334%	$245.1743	$245.17	$245.15	$245.20
Purchase #2	$39.88	7.195%	$42.7494	$42.75	$42.75	$42.70
Purchase #3	$45.56	10.356%	$50.2782	$50.28	$50.30	$50.30
Purchase #4	$186.69	5.291%	$196.5678	$196.57	$196.55	$196.60
Purchase #5	$232.75	9.314%	$254.4283	$254.43	$254.45	$254.40
Purchase #6	$31.49	4.188%	$32.8088	$32.81	$32.80	$32.80
Purchase #7	$92.70	12.301%	$104.103	$104.10	$104.10	$104.10
7 purchase totals =	$859.64		$926.1098	$926.11	$926.10	$926.10