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	$72.45	12.496%	$81.5034	$81.50	$81.50	$81.50
Purchase #2	$110.32	11.520%	$123.0289	$123.03	$123.05	$123.00
Purchase #3	$222.65	4.701%	$233.1168	$233.12	$233.10	$233.10
Purchase #4	$40.97	8.515%	$44.4586	$44.46	$44.45	$44.50
Purchase #5	$99.49	4.606%	$104.0725	$104.07	$104.05	$104.10
Purchase #6	$73.27	7.405%	$78.6956	$78.70	$78.70	$78.70
Purchase #7	$164.56	9.656%	$180.4499	$180.45	$180.45	$180.40
7 purchase totals =	$783.71		$845.3257	$845.33	$845.30	$845.30