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	$128.48	9.658%	$140.8886	$140.89	$140.90	$140.90
Purchase #2	$130.38	7.207%	$139.7765	$139.78	$139.80	$139.80
Purchase #3	$83.82	8.268%	$90.7502	$90.75	$90.75	$90.80
Purchase #4	$18.95	8.333%	$20.5291	$20.53	$20.55	$20.50
Purchase #5	$62.80	11.222%	$69.8474	$69.85	$69.85	$69.80
Purchase #6	$233.57	9.271%	$255.2243	$255.22	$255.20	$255.20
Purchase #7	$152.61	8.393%	$165.4186	$165.42	$165.40	$165.40
7 purchase totals =	$810.61		$882.4347	$882.44	$882.45	$882.40