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	$78.63	13.305%	$89.0917	$89.09	$89.10	$89.10
Purchase #2	$90.63	5.545%	$95.6554	$95.66	$95.65	$95.70
Purchase #3	$148.46	12.266%	$166.6701	$166.67	$166.65	$166.70
Purchase #4	$95.34	7.537%	$102.5258	$102.53	$102.55	$102.50
Purchase #5	$109.60	5.673%	$115.8176	$115.82	$115.80	$115.80
Purchase #6	$178.88	4.721%	$187.3249	$187.32	$187.30	$187.30
Purchase #7	$175.98	7.140%	$188.545	$188.55	$188.55	$188.50
7 purchase totals =	$877.52		$945.6305	$945.64	$945.60	$945.60