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	$210.80	9.293%	$230.3896	$230.39	$230.40	$230.40
Purchase #2	$133.83	12.851%	$151.0285	$151.03	$151.05	$151.00
Purchase #3	$113.86	5.659%	$120.3033	$120.30	$120.30	$120.30
Purchase #4	$188.41	6.504%	$200.6642	$200.66	$200.65	$200.70
Purchase #5	$77.52	3.297%	$80.0758	$80.08	$80.10	$80.10
Purchase #6	$69.74	11.782%	$77.9568	$77.96	$77.95	$78.00
Purchase #7	$131.53	7.661%	$141.6065	$141.61	$141.60	$141.60
7 purchase totals =	$925.69		$1,002.0247	$1,002.03	$1,002.05	$1,002.10