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	$190.59	11.182%	$211.9018	$211.90	$211.90	$211.90
Purchase #2	$99.32	5.623%	$104.9048	$104.90	$104.90	$104.90
Purchase #3	$177.53	9.621%	$194.6102	$194.61	$194.60	$194.60
Purchase #4	$40.72	3.191%	$42.0194	$42.02	$42.00	$42.00
Purchase #5	$235.90	9.255%	$257.7325	$257.73	$257.75	$257.70
Purchase #6	$183.84	3.258%	$189.8295	$189.83	$189.85	$189.80
Purchase #7	$91.31	7.804%	$98.4358	$98.44	$98.45	$98.40
7 purchase totals =	$1,019.21		$1,099.4340	$1,099.43	$1,099.45	$1,099.30