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	$88.54	13.404%	$100.4079	$100.41	$100.40	$100.40
Purchase #2	$173.95	6.631%	$185.4846	$185.48	$185.50	$185.50
Purchase #3	$153.89	3.620%	$159.4608	$159.46	$159.45	$159.50
Purchase #4	$115.35	3.489%	$119.3746	$119.37	$119.35	$119.40
Purchase #5	$92.35	4.609%	$96.6064	$96.61	$96.60	$96.60
Purchase #6	$234.38	8.558%	$254.4382	$254.44	$254.45	$254.40
Purchase #7	$58.74	12.675%	$66.1853	$66.19	$66.20	$66.20
7 purchase totals =	$917.20		$981.9578	$981.96	$981.95	$982.00