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	$169.37	8.269%	$183.3752	$183.38	$183.40	$183.40
Purchase #2	$40.32	12.516%	$45.3665	$45.37	$45.35	$45.40
Purchase #3	$54.40	13.554%	$61.7734	$61.77	$61.75	$61.80
Purchase #4	$102.45	7.681%	$110.3192	$110.32	$110.30	$110.30
Purchase #5	$156.54	11.405%	$174.3934	$174.39	$174.40	$174.40
Purchase #6	$18.86	10.463%	$20.8333	$20.83	$20.85	$20.80
Purchase #7	$33.76	12.732%	$38.0583	$38.06	$38.05	$38.10
7 purchase totals =	$575.70		$634.1193	$634.12	$634.10	$634.20