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	$73.45	11.816%	$82.1289	$82.13	$82.15	$82.10
Purchase #2	$131.77	12.161%	$147.7945	$147.79	$147.80	$147.80
Purchase #3	$128.45	4.374%	$134.0684	$134.07	$134.05	$134.10
Purchase #4	$153.43	11.777%	$171.4995	$171.50	$171.50	$171.50
Purchase #5	$245.30	10.637%	$271.3926	$271.39	$271.40	$271.40
Purchase #6	$70.46	10.619%	$77.9421	$77.94	$77.95	$77.90
Purchase #7	$113.27	11.726%	$126.552	$126.55	$126.55	$126.60
7 purchase totals =	$916.13		$1,011.3780	$1,011.37	$1,011.40	$1,011.40