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	$245.65	12.594%	$276.5872	$276.59	$276.60	$276.60
Purchase #2	$160.48	8.704%	$174.4482	$174.45	$174.45	$174.40
Purchase #3	$58.71	11.262%	$65.3219	$65.32	$65.30	$65.30
Purchase #4	$161.40	13.255%	$182.7936	$182.79	$182.80	$182.80
Purchase #5	$105.89	11.376%	$117.936	$117.94	$117.95	$117.90
Purchase #6	$91.61	8.238%	$99.1568	$99.16	$99.15	$99.20
Purchase #7	$94.37	4.112%	$98.2505	$98.25	$98.25	$98.30
7 purchase totals =	$918.11		$1,014.4942	$1,014.50	$1,014.50	$1,014.50