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	$107.72	11.319%	$119.9128	$119.91	$119.90	$119.90
Purchase #2	$37.59	12.813%	$42.4064	$42.41	$42.40	$42.40
Purchase #3	$198.95	8.591%	$216.0418	$216.04	$216.05	$216.00
Purchase #4	$230.57	7.259%	$247.3071	$247.31	$247.30	$247.30
Purchase #5	$126.55	5.252%	$133.1964	$133.20	$133.20	$133.20
Purchase #6	$139.72	3.399%	$144.4691	$144.47	$144.45	$144.50
Purchase #7	$101.45	11.874%	$113.4962	$113.50	$113.50	$113.50
7 purchase totals =	$942.55		$1,016.8298	$1,016.84	$1,016.80	$1,016.80