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	$139.53	6.340%	$148.3762	$148.38	$148.40	$148.40
Purchase #2	$225.67	10.642%	$249.6858	$249.69	$249.70	$249.70
Purchase #3	$132.71	10.238%	$146.2968	$146.30	$146.30	$146.30
Purchase #4	$92.49	7.649%	$99.5646	$99.56	$99.55	$99.60
Purchase #5	$51.71	3.546%	$53.5436	$53.54	$53.55	$53.50
Purchase #6	$90.76	12.277%	$101.9026	$101.90	$101.90	$101.90
Purchase #7	$88.48	4.217%	$92.2112	$92.21	$92.20	$92.20
7 purchase totals =	$821.35		$891.5808	$891.58	$891.60	$891.60