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	$33.89	5.669%	$35.8112	$35.81	$35.80	$35.80
Purchase #2	$162.61	12.630%	$183.1476	$183.15	$183.15	$183.10
Purchase #3	$153.39	7.807%	$165.3652	$165.37	$165.35	$165.40
Purchase #4	$176.49	10.230%	$194.5449	$194.54	$194.55	$194.50
Purchase #5	$81.85	12.842%	$92.3612	$92.36	$92.35	$92.40
Purchase #6	$245.87	10.256%	$271.0864	$271.09	$271.10	$271.10
Purchase #7	$147.95	5.659%	$156.3225	$156.32	$156.30	$156.30
7 purchase totals =	$1,002.05		$1,098.6390	$1,098.64	$1,098.60	$1,098.60