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	$236.34	8.529%	$256.4974	$256.50	$256.50	$256.50
Purchase #2	$148.71	7.803%	$160.3138	$160.31	$160.30	$160.30
Purchase #3	$65.84	10.766%	$72.9283	$72.93	$72.95	$72.90
Purchase #4	$93.56	10.226%	$103.1274	$103.13	$103.15	$103.10
Purchase #5	$169.59	3.163%	$174.9541	$174.95	$174.95	$175.00
Purchase #6	$65.36	12.150%	$73.3012	$73.30	$73.30	$73.30
Purchase #7	$156.53	6.330%	$166.4383	$166.44	$166.45	$166.40
7 purchase totals =	$935.93		$1,007.5605	$1,007.56	$1,007.60	$1,007.50