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	$27.69	3.313%	$28.6074	$28.61	$28.60	$28.60
Purchase #2	$149.85	6.382%	$159.4134	$159.41	$159.40	$159.40
Purchase #3	$150.95	4.510%	$157.7578	$157.76	$157.75	$157.80
Purchase #4	$110.45	13.590%	$125.4602	$125.46	$125.45	$125.50
Purchase #5	$37.72	10.314%	$41.6104	$41.61	$41.60	$41.60
Purchase #6	$163.38	3.114%	$168.4677	$168.47	$168.45	$168.50
Purchase #7	$55.32	7.392%	$59.4093	$59.41	$59.40	$59.40
7 purchase totals =	$695.36		$740.7262	$740.73	$740.65	$740.80