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	$38.25	3.172%	$39.4633	$39.46	$39.45	$39.50
Purchase #2	$96.44	6.576%	$102.7819	$102.78	$102.80	$102.80
Purchase #3	$66.50	7.652%	$71.5886	$71.59	$71.60	$71.60
Purchase #4	$155.91	7.846%	$168.1427	$168.14	$168.15	$168.10
Purchase #5	$81.27	11.149%	$90.3308	$90.33	$90.35	$90.30
Purchase #6	$23.65	9.468%	$25.8892	$25.89	$25.90	$25.90
Purchase #7	$76.67	12.809%	$86.4907	$86.49	$86.50	$86.50
7 purchase totals =	$538.69		$584.6872	$584.68	$584.75	$584.70