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	$70.28	11.765%	$78.5484	$78.55	$78.55	$78.50
Purchase #2	$114.90	9.750%	$126.1028	$126.10	$126.10	$126.10
Purchase #3	$91.59	8.719%	$99.5757	$99.58	$99.60	$99.60
Purchase #4	$45.36	4.820%	$47.5464	$47.55	$47.55	$47.50
Purchase #5	$170.95	8.698%	$185.8192	$185.82	$185.80	$185.80
Purchase #6	$11.58	7.850%	$12.489	$12.49	$12.50	$12.50
Purchase #7	$219.33	9.116%	$239.3241	$239.32	$239.30	$239.30
7 purchase totals =	$723.99		$789.4056	$789.41	$789.40	$789.30