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	$82.60	6.722%	$88.1524	$88.15	$88.15	$88.20
Purchase #2	$160.42	11.108%	$178.2395	$178.24	$178.25	$178.20
Purchase #3	$84.73	3.869%	$88.0082	$88.01	$88.00	$88.00
Purchase #4	$67.70	10.617%	$74.8877	$74.89	$74.90	$74.90
Purchase #5	$70.59	11.842%	$78.9493	$78.95	$78.95	$78.90
Purchase #6	$68.50	12.158%	$76.8282	$76.83	$76.85	$76.80
Purchase #7	$57.35	6.793%	$61.2458	$61.25	$61.25	$61.20
7 purchase totals =	$591.89		$646.3111	$646.32	$646.35	$646.20