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	$45.45	8.782%	$49.4414	$49.44	$49.45	$49.40
Purchase #2	$249.60	8.530%	$270.8909	$270.89	$270.90	$270.90
Purchase #3	$137.85	6.873%	$147.3244	$147.32	$147.30	$147.30
Purchase #4	$128.62	13.812%	$146.385	$146.39	$146.40	$146.40
Purchase #5	$111.35	10.771%	$123.3435	$123.34	$123.35	$123.30
Purchase #6	$180.91	7.465%	$194.4149	$194.41	$194.40	$194.40
Purchase #7	$70.33	4.280%	$73.3401	$73.34	$73.35	$73.30
7 purchase totals =	$924.11		$1,005.1402	$1,005.13	$1,005.15	$1,005.00