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	$53.40	10.781%	$59.1571	$59.16	$59.15	$59.20
Purchase #2	$135.91	4.372%	$141.852	$141.85	$141.85	$141.90
Purchase #3	$206.36	8.251%	$223.3868	$223.39	$223.40	$223.40
Purchase #4	$50.61	5.484%	$53.3855	$53.39	$53.40	$53.40
Purchase #5	$160.27	12.509%	$180.3182	$180.32	$180.30	$180.30
Purchase #6	$221.72	7.361%	$238.0408	$238.04	$238.05	$238.00
Purchase #7	$99.76	9.780%	$109.5165	$109.52	$109.50	$109.50
7 purchase totals =	$928.03		$1,005.6569	$1,005.67	$1,005.65	$1,005.70