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	$77.31	11.378%	$86.1063	$86.11	$86.10	$86.10
Purchase #2	$54.58	8.391%	$59.1598	$59.16	$59.15	$59.20
Purchase #3	$211.72	12.794%	$238.8075	$238.81	$238.80	$238.80
Purchase #4	$35.81	3.334%	$37.0039	$37.00	$37.00	$37.00
Purchase #5	$158.83	13.715%	$180.6135	$180.61	$180.60	$180.60
Purchase #6	$223.44	8.208%	$241.78	$241.78	$241.80	$241.80
Purchase #7	$156.58	13.495%	$177.7105	$177.71	$177.70	$177.70
7 purchase totals =	$918.27		$1,021.1815	$1,021.18	$1,021.15	$1,021.20