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	$69.52	13.501%	$78.9059	$78.91	$78.90	$78.90
Purchase #2	$108.71	10.353%	$119.9647	$119.96	$119.95	$120.00
Purchase #3	$240.40	9.393%	$262.9808	$262.98	$263.00	$263.00
Purchase #4	$111.33	6.352%	$118.4017	$118.40	$118.40	$118.40
Purchase #5	$94.81	5.806%	$100.3147	$100.31	$100.30	$100.30
Purchase #6	$86.62	8.869%	$94.3023	$94.30	$94.30	$94.30
Purchase #7	$141.89	10.537%	$156.8409	$156.84	$156.85	$156.80
7 purchase totals =	$853.28		$931.7110	$931.70	$931.70	$931.70