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	$29.58	9.401%	$32.3608	$32.36	$32.35	$32.40
Purchase #2	$218.50	5.120%	$229.6872	$229.69	$229.70	$229.70
Purchase #3	$161.86	5.393%	$170.5891	$170.59	$170.60	$170.60
Purchase #4	$156.95	5.103%	$164.9592	$164.96	$164.95	$165.00
Purchase #5	$83.82	6.724%	$89.4561	$89.46	$89.45	$89.50
Purchase #6	$176.71	8.445%	$191.6332	$191.63	$191.65	$191.60
Purchase #7	$233.54	13.871%	$265.9343	$265.93	$265.95	$265.90
7 purchase totals =	$1,060.96		$1,144.6199	$1,144.62	$1,144.65	$1,144.70