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	$222.85	5.535%	$235.1847	$235.18	$235.20	$235.20
Purchase #2	$59.88	9.689%	$65.6818	$65.68	$65.70	$65.70
Purchase #3	$96.79	7.208%	$103.7666	$103.77	$103.75	$103.80
Purchase #4	$140.25	7.154%	$150.2835	$150.28	$150.30	$150.30
Purchase #5	$249.48	4.728%	$261.2754	$261.28	$261.30	$261.30
Purchase #6	$105.86	4.871%	$111.0164	$111.02	$111.00	$111.00
Purchase #7	$35.96	7.753%	$38.748	$38.75	$38.75	$38.70
7 purchase totals =	$911.07		$965.9564	$965.96	$966.00	$966.00