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	$160.88	5.142%	$169.1524	$169.15	$169.15	$169.20
Purchase #2	$28.67	7.689%	$30.8744	$30.87	$30.85	$30.90
Purchase #3	$223.77	7.591%	$240.7564	$240.76	$240.75	$240.80
Purchase #4	$229.78	7.213%	$246.354	$246.35	$246.35	$246.40
Purchase #5	$79.96	13.442%	$90.7082	$90.71	$90.70	$90.70
Purchase #6	$80.82	11.249%	$89.9114	$89.91	$89.90	$89.90
Purchase #7	$49.72	10.110%	$54.7467	$54.75	$54.75	$54.70
7 purchase totals =	$853.60		$922.5035	$922.50	$922.45	$922.60