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	$141.50	8.772%	$153.9124	$153.91	$153.90	$153.90
Purchase #2	$236.86	12.278%	$265.9417	$265.94	$265.95	$265.90
Purchase #3	$72.33	10.130%	$79.657	$79.66	$79.65	$79.70
Purchase #4	$137.67	10.869%	$152.6334	$152.63	$152.65	$152.60
Purchase #5	$40.35	4.575%	$42.196	$42.20	$42.20	$42.20
Purchase #6	$58.28	10.709%	$64.5212	$64.52	$64.50	$64.50
Purchase #7	$7.55	3.723%	$7.8311	$7.83	$7.85	$7.80
7 purchase totals =	$694.54		$766.6928	$766.69	$766.70	$766.60