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	$19.46	4.542%	$20.3439	$20.34	$20.35	$20.30
Purchase #2	$205.42	8.682%	$223.2546	$223.25	$223.25	$223.30
Purchase #3	$132.56	5.135%	$139.367	$139.37	$139.35	$139.40
Purchase #4	$70.82	4.662%	$74.1216	$74.12	$74.10	$74.10
Purchase #5	$96.45	3.166%	$99.5036	$99.50	$99.50	$99.50
Purchase #6	$172.56	9.444%	$188.8566	$188.86	$188.85	$188.90
Purchase #7	$236.31	12.211%	$265.1658	$265.17	$265.15	$265.20
7 purchase totals =	$933.58		$1,010.6131	$1,010.61	$1,010.55	$1,010.70