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	$243.41	9.323%	$266.1031	$266.10	$266.10	$266.10
Purchase #2	$128.72	13.538%	$146.1461	$146.15	$146.15	$146.10
Purchase #3	$56.47	10.157%	$62.2057	$62.21	$62.20	$62.20
Purchase #4	$227.28	11.422%	$253.2399	$253.24	$253.25	$253.20
Purchase #5	$100.53	10.584%	$111.1701	$111.17	$111.15	$111.20
Purchase #6	$190.29	10.646%	$210.5483	$210.55	$210.55	$210.50
Purchase #7	$104.68	7.511%	$112.5425	$112.54	$112.55	$112.50
7 purchase totals =	$1,051.38		$1,161.9557	$1,161.96	$1,161.95	$1,161.80