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	$123.66	9.460%	$135.3582	$135.36	$135.35	$135.40
Purchase #2	$247.95	13.229%	$280.7513	$280.75	$280.75	$280.80
Purchase #3	$123.26	6.535%	$131.315	$131.32	$131.30	$131.30
Purchase #4	$30.38	10.611%	$33.6036	$33.60	$33.60	$33.60
Purchase #5	$78.60	13.788%	$89.4374	$89.44	$89.45	$89.40
Purchase #6	$105.92	8.354%	$114.7686	$114.77	$114.75	$114.80
Purchase #7	$52.54	11.498%	$58.581	$58.58	$58.60	$58.60
7 purchase totals =	$762.31		$843.8151	$843.82	$843.80	$843.90