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	$53.49	6.608%	$57.0246	$57.02	$57.00	$57.00
Purchase #2	$173.40	12.229%	$194.6051	$194.61	$194.60	$194.60
Purchase #3	$80.75	11.315%	$89.8869	$89.89	$89.90	$89.90
Purchase #4	$29.57	9.402%	$32.3502	$32.35	$32.35	$32.40
Purchase #5	$30.40	7.184%	$32.5839	$32.58	$32.60	$32.60
Purchase #6	$87.80	12.730%	$98.9769	$98.98	$99.00	$99.00
Purchase #7	$29.49	7.724%	$31.7678	$31.77	$31.75	$31.80
7 purchase totals =	$484.90		$537.1954	$537.20	$537.20	$537.30