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	$169.90	12.852%	$191.7355	$191.74	$191.75	$191.70
Purchase #2	$78.45	5.144%	$82.4855	$82.49	$82.50	$82.50
Purchase #3	$141.91	9.171%	$154.9246	$154.92	$154.90	$154.90
Purchase #4	$146.32	4.515%	$152.9263	$152.93	$152.95	$152.90
Purchase #5	$232.65	10.708%	$257.5622	$257.56	$257.55	$257.60
Purchase #6	$42.66	9.756%	$46.8219	$46.82	$46.80	$46.80
Purchase #7	$40.33	12.536%	$45.3858	$45.39	$45.40	$45.40
7 purchase totals =	$852.22		$931.8418	$931.85	$931.85	$931.80