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	$81.36	6.138%	$86.3539	$86.35	$86.35	$86.40
Purchase #2	$100.57	10.527%	$111.157	$111.16	$111.15	$111.20
Purchase #3	$144.81	4.555%	$151.4061	$151.41	$151.40	$151.40
Purchase #4	$16.74	8.758%	$18.2061	$18.21	$18.20	$18.20
Purchase #5	$131.79	3.150%	$135.9414	$135.94	$135.95	$135.90
Purchase #6	$51.49	11.344%	$57.331	$57.33	$57.35	$57.30
Purchase #7	$57.62	3.633%	$59.7133	$59.71	$59.70	$59.70
7 purchase totals =	$584.38		$620.1088	$620.11	$620.10	$620.10