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	$150.64	6.651%	$160.6591	$160.66	$160.65	$160.70
Purchase #2	$242.86	7.684%	$261.5214	$261.52	$261.50	$261.50
Purchase #3	$54.84	12.433%	$61.6583	$61.66	$61.65	$61.70
Purchase #4	$50.39	12.208%	$56.5416	$56.54	$56.55	$56.50
Purchase #5	$85.34	12.558%	$96.057	$96.06	$96.05	$96.10
Purchase #6	$204.79	11.340%	$228.0132	$228.01	$228.00	$228.00
Purchase #7	$141.77	7.425%	$152.2964	$152.30	$152.30	$152.30
7 purchase totals =	$930.63		$1,016.7470	$1,016.75	$1,016.70	$1,016.80