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	$90.81	3.696%	$94.1663	$94.17	$94.15	$94.20
Purchase #2	$79.94	10.295%	$88.1698	$88.17	$88.15	$88.20
Purchase #3	$166.50	11.422%	$185.5176	$185.52	$185.50	$185.50
Purchase #4	$72.48	11.624%	$80.9051	$80.91	$80.90	$80.90
Purchase #5	$137.63	10.265%	$151.7577	$151.76	$151.75	$151.80
Purchase #6	$211.87	12.342%	$238.019	$238.02	$238.00	$238.00
Purchase #7	$83.52	4.661%	$87.4129	$87.41	$87.40	$87.40
7 purchase totals =	$842.75		$925.9484	$925.96	$925.85	$926.00