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	$32.39	10.689%	$35.8522	$35.85	$35.85	$35.90
Purchase #2	$83.52	10.585%	$92.3606	$92.36	$92.35	$92.40
Purchase #3	$125.39	11.109%	$139.3196	$139.32	$139.30	$139.30
Purchase #4	$50.75	3.215%	$52.3816	$52.38	$52.40	$52.40
Purchase #5	$90.64	4.705%	$94.9046	$94.90	$94.90	$94.90
Purchase #6	$226.36	4.501%	$236.5485	$236.55	$236.55	$236.50
Purchase #7	$73.33	6.483%	$78.084	$78.08	$78.10	$78.10
7 purchase totals =	$682.38		$729.4511	$729.44	$729.45	$729.50