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	$79.76	13.561%	$90.5763	$90.58	$90.60	$90.60
Purchase #2	$204.68	11.834%	$228.9018	$228.90	$228.90	$228.90
Purchase #3	$81.48	12.656%	$91.7921	$91.79	$91.80	$91.80
Purchase #4	$245.43	9.475%	$268.6845	$268.68	$268.70	$268.70
Purchase #5	$196.77	13.256%	$222.8538	$222.85	$222.85	$222.90
Purchase #6	$165.37	4.413%	$172.6678	$172.67	$172.65	$172.70
Purchase #7	$213.38	9.643%	$233.9562	$233.96	$233.95	$234.00
7 purchase totals =	$1,186.87		$1,309.4325	$1,309.43	$1,309.45	$1,309.60