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	$18.48	12.819%	$20.849	$20.85	$20.85	$20.80
Purchase #2	$179.50	11.863%	$200.7941	$200.79	$200.80	$200.80
Purchase #3	$154.88	12.816%	$174.7294	$174.73	$174.75	$174.70
Purchase #4	$141.30	10.799%	$156.559	$156.56	$156.55	$156.60
Purchase #5	$95.49	8.626%	$103.727	$103.73	$103.75	$103.70
Purchase #6	$200.82	7.313%	$215.506	$215.51	$215.50	$215.50
Purchase #7	$189.88	10.646%	$210.0946	$210.09	$210.10	$210.10
7 purchase totals =	$980.35		$1,082.2591	$1,082.26	$1,082.30	$1,082.20