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	$37.92	6.391%	$40.3435	$40.34	$40.35	$40.30
Purchase #2	$73.47	6.831%	$78.4887	$78.49	$78.50	$78.50
Purchase #3	$147.82	10.281%	$163.0174	$163.02	$163.00	$163.00
Purchase #4	$164.38	4.271%	$171.4007	$171.40	$171.40	$171.40
Purchase #5	$142.43	6.681%	$151.9457	$151.95	$151.95	$151.90
Purchase #6	$209.69	8.327%	$227.1509	$227.15	$227.15	$227.20
Purchase #7	$173.99	8.338%	$188.4973	$188.50	$188.50	$188.50
7 purchase totals =	$949.70		$1,020.8442	$1,020.85	$1,020.85	$1,020.80