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	$124.67	10.263%	$137.4649	$137.46	$137.45	$137.50
Purchase #2	$100.32	4.557%	$104.8916	$104.89	$104.90	$104.90
Purchase #3	$163.69	9.449%	$179.1571	$179.16	$179.15	$179.20
Purchase #4	$122.77	4.710%	$128.5525	$128.55	$128.55	$128.60
Purchase #5	$142.52	10.672%	$157.7297	$157.73	$157.75	$157.70
Purchase #6	$17.65	3.497%	$18.2672	$18.27	$18.25	$18.30
Purchase #7	$91.47	7.871%	$98.6696	$98.67	$98.65	$98.70
7 purchase totals =	$763.09		$824.7326	$824.73	$824.70	$824.90