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	$236.58	5.684%	$250.0272	$250.03	$250.05	$250.00
Purchase #2	$103.51	13.414%	$117.3948	$117.39	$117.40	$117.40
Purchase #3	$45.90	10.835%	$50.8733	$50.87	$50.85	$50.90
Purchase #4	$245.51	3.792%	$254.8197	$254.82	$254.80	$254.80
Purchase #5	$154.79	9.152%	$168.9564	$168.96	$168.95	$169.00
Purchase #6	$44.41	13.154%	$50.2517	$50.25	$50.25	$50.30
Purchase #7	$96.97	9.156%	$105.8486	$105.85	$105.85	$105.80
7 purchase totals =	$927.67		$998.1717	$998.17	$998.15	$998.20