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	$180.44	6.343%	$191.8853	$191.89	$191.90	$191.90
Purchase #2	$214.76	8.861%	$233.7899	$233.79	$233.80	$233.80
Purchase #3	$72.90	13.603%	$82.8166	$82.82	$82.80	$82.80
Purchase #4	$25.62	13.726%	$29.1366	$29.14	$29.15	$29.10
Purchase #5	$209.58	7.389%	$225.0659	$225.07	$225.05	$225.10
Purchase #6	$123.67	7.618%	$133.0912	$133.09	$133.10	$133.10
Purchase #7	$73.50	9.800%	$80.703	$80.70	$80.70	$80.70
7 purchase totals =	$900.47		$976.4885	$976.50	$976.50	$976.50