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	$89.63	12.262%	$100.6204	$100.62	$100.60	$100.60
Purchase #2	$83.89	13.828%	$95.4903	$95.49	$95.50	$95.50
Purchase #3	$186.47	13.633%	$211.8915	$211.89	$211.90	$211.90
Purchase #4	$166.31	11.799%	$185.9329	$185.93	$185.95	$185.90
Purchase #5	$209.57	5.673%	$221.4589	$221.46	$221.45	$221.50
Purchase #6	$58.69	7.129%	$62.874	$62.87	$62.85	$62.90
Purchase #7	$151.44	3.510%	$156.7555	$156.76	$156.75	$156.80
7 purchase totals =	$946.00		$1,035.0235	$1,035.02	$1,035.00	$1,035.10