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	$159.57	5.394%	$168.1772	$168.18	$168.20	$168.20
Purchase #2	$147.78	8.364%	$160.1403	$160.14	$160.15	$160.10
Purchase #3	$125.89	12.361%	$141.4513	$141.45	$141.45	$141.50
Purchase #4	$162.49	10.228%	$179.1095	$179.11	$179.10	$179.10
Purchase #5	$98.72	9.490%	$108.0885	$108.09	$108.10	$108.10
Purchase #6	$175.78	11.864%	$196.6345	$196.63	$196.65	$196.60
Purchase #7	$70.37	13.378%	$79.7841	$79.78	$79.80	$79.80
7 purchase totals =	$940.60		$1,033.3854	$1,033.38	$1,033.45	$1,033.40