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	$59.71	11.267%	$66.4375	$66.44	$66.45	$66.40
Purchase #2	$124.90	12.264%	$140.2177	$140.22	$140.20	$140.20
Purchase #3	$20.66	4.717%	$21.6345	$21.63	$21.65	$21.60
Purchase #4	$227.73	12.220%	$255.5586	$255.56	$255.55	$255.60
Purchase #5	$187.39	12.216%	$210.2816	$210.28	$210.30	$210.30
Purchase #6	$155.40	13.445%	$176.2935	$176.29	$176.30	$176.30
Purchase #7	$126.72	11.667%	$141.5044	$141.50	$141.50	$141.50
7 purchase totals =	$902.51		$1,011.9278	$1,011.92	$1,011.95	$1,011.90