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	$235.36	6.297%	$250.1806	$250.18	$250.20	$250.20
Purchase #2	$240.88	9.642%	$264.1056	$264.11	$264.10	$264.10
Purchase #3	$47.59	11.334%	$52.9839	$52.98	$53.00	$53.00
Purchase #4	$72.82	10.480%	$80.4515	$80.45	$80.45	$80.50
Purchase #5	$103.79	12.549%	$116.8146	$116.81	$116.80	$116.80
Purchase #6	$65.48	10.105%	$72.0968	$72.10	$72.10	$72.10
Purchase #7	$125.50	6.759%	$133.9825	$133.98	$134.00	$134.00
7 purchase totals =	$891.42		$970.6155	$970.61	$970.65	$970.70