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	$86.52	4.672%	$90.5622	$90.56	$90.55	$90.60
Purchase #2	$159.39	12.610%	$179.4891	$179.49	$179.50	$179.50
Purchase #3	$135.46	7.765%	$145.9785	$145.98	$146.00	$146.00
Purchase #4	$108.93	6.125%	$115.602	$115.60	$115.60	$115.60
Purchase #5	$100.76	3.437%	$104.2231	$104.22	$104.20	$104.20
Purchase #6	$178.56	3.723%	$185.2078	$185.21	$185.20	$185.20
Purchase #7	$100.59	3.840%	$104.4527	$104.45	$104.45	$104.50
7 purchase totals =	$870.21		$925.5154	$925.51	$925.50	$925.60