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	$207.53	3.686%	$215.1796	$215.18	$215.20	$215.20
Purchase #2	$154.65	13.533%	$175.5788	$175.58	$175.60	$175.60
Purchase #3	$125.61	12.184%	$140.9143	$140.91	$140.90	$140.90
Purchase #4	$68.86	5.110%	$72.3787	$72.38	$72.40	$72.40
Purchase #5	$166.46	7.546%	$179.0211	$179.02	$179.00	$179.00
Purchase #6	$22.71	10.760%	$25.1536	$25.15	$25.15	$25.20
Purchase #7	$152.58	11.605%	$170.2869	$170.29	$170.30	$170.30
7 purchase totals =	$898.40		$978.5130	$978.51	$978.55	$978.60