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	$89.60	11.510%	$99.913	$99.91	$99.90	$99.90
Purchase #2	$149.32	12.205%	$167.5445	$167.54	$167.55	$167.50
Purchase #3	$37.34	3.722%	$38.7298	$38.73	$38.75	$38.70
Purchase #4	$154.70	10.208%	$170.4918	$170.49	$170.50	$170.50
Purchase #5	$209.77	5.140%	$220.5522	$220.55	$220.55	$220.60
Purchase #6	$232.58	10.820%	$257.7452	$257.75	$257.75	$257.70
Purchase #7	$79.81	3.500%	$82.6034	$82.60	$82.60	$82.60
7 purchase totals =	$953.12		$1,037.5799	$1,037.57	$1,037.60	$1,037.50