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	$134.60	10.345%	$148.5244	$148.52	$148.50	$148.50
Purchase #2	$204.68	11.211%	$227.6267	$227.63	$227.65	$227.60
Purchase #3	$240.90	11.637%	$268.9335	$268.93	$268.95	$268.90
Purchase #4	$227.93	5.423%	$240.2906	$240.29	$240.30	$240.30
Purchase #5	$15.76	3.630%	$16.3321	$16.33	$16.35	$16.30
Purchase #6	$38.62	13.242%	$43.7341	$43.73	$43.75	$43.70
Purchase #7	$56.87	4.815%	$59.6083	$59.61	$59.60	$59.60
7 purchase totals =	$919.36		$1,005.0497	$1,005.04	$1,005.10	$1,004.90