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	$42.51	12.306%	$47.7413	$47.74	$47.75	$47.70
Purchase #2	$50.64	3.802%	$52.5653	$52.57	$52.55	$52.60
Purchase #3	$98.37	4.413%	$102.7111	$102.71	$102.70	$102.70
Purchase #4	$81.77	11.283%	$90.9961	$91.00	$91.00	$91.00
Purchase #5	$35.96	8.152%	$38.8915	$38.89	$38.90	$38.90
Purchase #6	$154.91	10.612%	$171.349	$171.35	$171.35	$171.30
Purchase #7	$238.42	7.303%	$255.8318	$255.83	$255.85	$255.80
7 purchase totals =	$702.58		$760.0861	$760.09	$760.10	$760.00