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	$32.84	3.363%	$33.9444	$33.94	$33.95	$33.90
Purchase #2	$70.95	10.439%	$78.3565	$78.36	$78.35	$78.40
Purchase #3	$206.40	11.219%	$229.556	$229.56	$229.55	$229.60
Purchase #4	$51.87	3.867%	$53.8758	$53.88	$53.90	$53.90
Purchase #5	$60.68	10.146%	$66.8366	$66.84	$66.85	$66.80
Purchase #6	$75.99	6.625%	$81.0243	$81.02	$81.00	$81.00
Purchase #7	$116.94	5.570%	$123.4536	$123.45	$123.45	$123.50
7 purchase totals =	$615.67		$667.0472	$667.05	$667.05	$667.10