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	$171.80	10.528%	$189.8871	$189.89	$189.90	$189.90
Purchase #2	$82.43	11.268%	$91.7182	$91.72	$91.70	$91.70
Purchase #3	$62.72	9.392%	$68.6107	$68.61	$68.60	$68.60
Purchase #4	$81.79	13.196%	$92.583	$92.58	$92.60	$92.60
Purchase #5	$75.83	4.818%	$79.4835	$79.48	$79.50	$79.50
Purchase #6	$14.81	4.728%	$15.5102	$15.51	$15.50	$15.50
Purchase #7	$85.25	12.718%	$96.0921	$96.09	$96.10	$96.10
7 purchase totals =	$574.63		$633.8848	$633.88	$633.90	$633.90