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	$89.35	10.758%	$98.9623	$98.96	$98.95	$99.00
Purchase #2	$66.72	11.342%	$74.2874	$74.29	$74.30	$74.30
Purchase #3	$28.71	11.601%	$32.0406	$32.04	$32.05	$32.00
Purchase #4	$242.89	13.127%	$274.7742	$274.77	$274.75	$274.80
Purchase #5	$29.48	9.654%	$32.326	$32.33	$32.35	$32.30
Purchase #6	$54.74	4.270%	$57.0774	$57.08	$57.10	$57.10
Purchase #7	$133.77	10.574%	$147.9148	$147.91	$147.90	$147.90
7 purchase totals =	$645.66		$717.3827	$717.38	$717.40	$717.40