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	$39.28	6.637%	$41.887	$41.89	$41.90	$41.90
Purchase #2	$176.71	13.596%	$200.7355	$200.74	$200.75	$200.70
Purchase #3	$241.61	10.694%	$267.4478	$267.45	$267.45	$267.40
Purchase #4	$142.79	5.751%	$151.0019	$151.00	$151.00	$151.00
Purchase #5	$43.53	7.473%	$46.783	$46.78	$46.80	$46.80
Purchase #6	$85.78	8.606%	$93.1622	$93.16	$93.15	$93.20
Purchase #7	$55.47	7.739%	$59.7628	$59.76	$59.75	$59.80
7 purchase totals =	$785.17		$860.7802	$860.78	$860.80	$860.80