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	$32.78	13.539%	$37.2181	$37.22	$37.20	$37.20
Purchase #2	$247.90	9.404%	$271.2125	$271.21	$271.20	$271.20
Purchase #3	$142.98	4.113%	$148.8608	$148.86	$148.85	$148.90
Purchase #4	$101.35	13.654%	$115.1883	$115.19	$115.20	$115.20
Purchase #5	$139.35	9.570%	$152.6858	$152.69	$152.70	$152.70
Purchase #6	$78.30	4.631%	$81.9261	$81.93	$81.95	$81.90
Purchase #7	$67.90	5.695%	$71.7669	$71.77	$71.75	$71.80
7 purchase totals =	$810.56		$878.8585	$878.87	$878.85	$878.90