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	$90.50	10.398%	$99.9102	$99.91	$99.90	$99.90
Purchase #2	$52.28	6.583%	$55.7216	$55.72	$55.70	$55.70
Purchase #3	$16.83	11.757%	$18.8087	$18.81	$18.80	$18.80
Purchase #4	$238.48	11.619%	$266.189	$266.19	$266.20	$266.20
Purchase #5	$216.74	11.823%	$242.3652	$242.37	$242.35	$242.40
Purchase #6	$196.33	4.794%	$205.7421	$205.74	$205.75	$205.70
Purchase #7	$78.53	13.312%	$88.9839	$88.98	$89.00	$89.00
7 purchase totals =	$889.69		$977.7207	$977.72	$977.70	$977.70