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	$35.51	6.531%	$37.8292	$37.83	$37.85	$37.80
Purchase #2	$82.77	13.627%	$94.0491	$94.05	$94.05	$94.00
Purchase #3	$102.25	8.653%	$111.0977	$111.10	$111.10	$111.10
Purchase #4	$58.25	6.440%	$62.0013	$62.00	$62.00	$62.00
Purchase #5	$142.64	6.145%	$151.4052	$151.41	$151.40	$151.40
Purchase #6	$150.38	11.557%	$167.7594	$167.76	$167.75	$167.80
Purchase #7	$244.31	9.443%	$267.3802	$267.38	$267.40	$267.40
7 purchase totals =	$816.11		$891.5221	$891.53	$891.55	$891.50