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	$113.95	13.727%	$129.5919	$129.59	$129.60	$129.60
Purchase #2	$96.73	6.142%	$102.6712	$102.67	$102.65	$102.70
Purchase #3	$221.36	11.180%	$246.108	$246.11	$246.10	$246.10
Purchase #4	$230.69	12.145%	$258.7073	$258.71	$258.70	$258.70
Purchase #5	$74.69	4.439%	$78.0055	$78.01	$78.00	$78.00
Purchase #6	$85.68	5.801%	$90.6503	$90.65	$90.65	$90.70
Purchase #7	$65.25	3.552%	$67.5677	$67.57	$67.55	$67.60
7 purchase totals =	$888.35		$973.3019	$973.31	$973.25	$973.40