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	$52.87	9.720%	$58.009	$58.01	$58.00	$58.00
Purchase #2	$159.58	4.516%	$166.7866	$166.79	$166.80	$166.80
Purchase #3	$135.95	12.438%	$152.8595	$152.86	$152.85	$152.90
Purchase #4	$59.61	3.620%	$61.7679	$61.77	$61.75	$61.80
Purchase #5	$237.95	10.695%	$263.3988	$263.40	$263.40	$263.40
Purchase #6	$25.59	12.322%	$28.7432	$28.74	$28.75	$28.70
Purchase #7	$118.59	7.469%	$127.4475	$127.45	$127.45	$127.40
7 purchase totals =	$790.14		$859.0125	$859.02	$859.00	$859.00