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	$166.88	10.651%	$184.6544	$184.65	$184.65	$184.70
Purchase #2	$23.99	6.586%	$25.57	$25.57	$25.55	$25.60
Purchase #3	$91.83	10.568%	$101.5346	$101.53	$101.55	$101.50
Purchase #4	$85.97	5.163%	$90.4086	$90.41	$90.40	$90.40
Purchase #5	$44.96	6.804%	$48.0191	$48.02	$48.00	$48.00
Purchase #6	$41.34	9.196%	$45.1416	$45.14	$45.15	$45.10
Purchase #7	$52.38	7.434%	$56.2739	$56.27	$56.25	$56.30
7 purchase totals =	$507.35		$551.6022	$551.59	$551.55	$551.60