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	$219.92	6.377%	$233.9443	$233.94	$233.95	$233.90
Purchase #2	$90.95	8.205%	$98.4124	$98.41	$98.40	$98.40
Purchase #3	$139.33	5.669%	$147.2286	$147.23	$147.25	$147.20
Purchase #4	$77.25	6.262%	$82.0874	$82.09	$82.10	$82.10
Purchase #5	$23.77	7.179%	$25.4764	$25.48	$25.50	$25.50
Purchase #6	$209.65	8.531%	$227.5352	$227.54	$227.55	$227.50
Purchase #7	$248.33	10.787%	$275.1174	$275.12	$275.10	$275.10
7 purchase totals =	$1,009.20		$1,089.8017	$1,089.81	$1,089.85	$1,089.70