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	$17.59	7.509%	$18.9108	$18.91	$18.90	$18.90
Purchase #2	$93.58	3.503%	$96.8581	$96.86	$96.85	$96.90
Purchase #3	$226.88	10.262%	$250.1624	$250.16	$250.15	$250.20
Purchase #4	$99.59	5.847%	$105.413	$105.41	$105.40	$105.40
Purchase #5	$78.52	5.359%	$82.7279	$82.73	$82.75	$82.70
Purchase #6	$169.92	5.738%	$179.67	$179.67	$179.65	$179.70
Purchase #7	$69.41	12.136%	$77.8336	$77.83	$77.85	$77.80
7 purchase totals =	$755.49		$811.5758	$811.57	$811.55	$811.60