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	$46.89	13.852%	$53.3852	$53.39	$53.40	$53.40
Purchase #2	$243.79	6.604%	$259.8899	$259.89	$259.90	$259.90
Purchase #3	$79.44	7.414%	$85.3297	$85.33	$85.35	$85.30
Purchase #4	$174.36	8.455%	$189.1021	$189.10	$189.10	$189.10
Purchase #5	$122.62	8.105%	$132.5584	$132.56	$132.55	$132.60
Purchase #6	$158.28	5.301%	$166.6704	$166.67	$166.65	$166.70
Purchase #7	$35.76	7.601%	$38.4781	$38.48	$38.50	$38.50
7 purchase totals =	$861.14		$925.4138	$925.42	$925.45	$925.50