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	$84.70	7.479%	$91.0347	$91.03	$91.05	$91.00
Purchase #2	$142.94	8.534%	$155.1385	$155.14	$155.15	$155.10
Purchase #3	$78.43	6.572%	$83.5844	$83.58	$83.60	$83.60
Purchase #4	$218.76	10.828%	$242.4473	$242.45	$242.45	$242.40
Purchase #5	$9.69	11.639%	$10.8178	$10.82	$10.80	$10.80
Purchase #6	$227.78	6.171%	$241.8363	$241.84	$241.85	$241.80
Purchase #7	$29.32	8.656%	$31.8579	$31.86	$31.85	$31.90
7 purchase totals =	$791.62		$856.7169	$856.72	$856.75	$856.60