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	$189.67	4.491%	$198.1881	$198.19	$198.20	$198.20
Purchase #2	$224.53	13.784%	$255.4792	$255.48	$255.50	$255.50
Purchase #3	$76.39	12.867%	$86.2191	$86.22	$86.20	$86.20
Purchase #4	$147.33	11.551%	$164.3481	$164.35	$164.35	$164.30
Purchase #5	$110.89	6.492%	$118.089	$118.09	$118.10	$118.10
Purchase #6	$66.52	8.859%	$72.413	$72.41	$72.40	$72.40
Purchase #7	$29.79	8.252%	$32.2483	$32.25	$32.25	$32.20
7 purchase totals =	$845.12		$926.9848	$926.99	$927.00	$926.90