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	$133.32	12.538%	$150.0357	$150.04	$150.05	$150.00
Purchase #2	$61.95	13.614%	$70.3839	$70.38	$70.40	$70.40
Purchase #3	$104.97	6.566%	$111.8623	$111.86	$111.85	$111.90
Purchase #4	$76.59	4.780%	$80.251	$80.25	$80.25	$80.30
Purchase #5	$132.71	6.519%	$141.3614	$141.36	$141.35	$141.40
Purchase #6	$71.71	13.227%	$81.1951	$81.20	$81.20	$81.20
Purchase #7	$206.86	10.821%	$229.2443	$229.24	$229.25	$229.20
7 purchase totals =	$788.11		$864.3337	$864.33	$864.35	$864.40