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	$149.53	12.372%	$168.0299	$168.03	$168.05	$168.00
Purchase #2	$39.58	12.134%	$44.3826	$44.38	$44.40	$44.40
Purchase #3	$198.81	10.389%	$219.4644	$219.46	$219.45	$219.50
Purchase #4	$33.31	7.676%	$35.8669	$35.87	$35.85	$35.90
Purchase #5	$76.95	7.237%	$82.5189	$82.52	$82.50	$82.50
Purchase #6	$65.35	6.359%	$69.5056	$69.51	$69.50	$69.50
Purchase #7	$49.89	7.668%	$53.7156	$53.72	$53.70	$53.70
7 purchase totals =	$613.42		$673.4839	$673.49	$673.45	$673.50