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	$74.87	10.171%	$82.485	$82.49	$82.50	$82.50
Purchase #2	$49.34	9.537%	$54.0456	$54.05	$54.05	$54.00
Purchase #3	$60.82	4.644%	$63.6445	$63.64	$63.65	$63.60
Purchase #4	$206.98	7.528%	$222.5615	$222.56	$222.55	$222.60
Purchase #5	$28.54	11.478%	$31.8158	$31.82	$31.80	$31.80
Purchase #6	$158.27	5.412%	$166.8356	$166.84	$166.85	$166.80
Purchase #7	$174.45	7.489%	$187.5146	$187.51	$187.50	$187.50
7 purchase totals =	$753.27		$808.9026	$808.91	$808.90	$808.80