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	$17.31	8.676%	$18.8118	$18.81	$18.80	$18.80
Purchase #2	$165.69	10.668%	$183.3658	$183.37	$183.35	$183.40
Purchase #3	$46.69	12.404%	$52.4814	$52.48	$52.50	$52.50
Purchase #4	$189.74	10.529%	$209.7177	$209.72	$209.70	$209.70
Purchase #5	$58.90	13.625%	$66.9251	$66.93	$66.95	$66.90
Purchase #6	$68.80	11.790%	$76.9115	$76.91	$76.90	$76.90
Purchase #7	$19.34	7.130%	$20.7189	$20.72	$20.70	$20.70
7 purchase totals =	$566.47		$628.9322	$628.94	$628.90	$628.90