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	$7.83	11.367%	$8.72	$8.72	$8.70	$8.70
Purchase #2	$19.54	11.142%	$21.7171	$21.72	$21.70	$21.70
Purchase #3	$103.67	8.147%	$112.116	$112.12	$112.10	$112.10
Purchase #4	$155.79	9.796%	$171.0512	$171.05	$171.05	$171.10
Purchase #5	$131.40	5.187%	$138.2157	$138.22	$138.20	$138.20
Purchase #6	$65.91	9.318%	$72.0515	$72.05	$72.05	$72.10
Purchase #7	$163.73	4.740%	$171.4908	$171.49	$171.50	$171.50
7 purchase totals =	$647.87		$695.3623	$695.37	$695.30	$695.40