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	$25.46	3.392%	$26.3236	$26.32	$26.30	$26.30
Purchase #2	$56.70	13.865%	$64.5615	$64.56	$64.55	$64.60
Purchase #3	$149.62	12.696%	$168.6158	$168.62	$168.60	$168.60
Purchase #4	$109.42	7.742%	$117.8913	$117.89	$117.90	$117.90
Purchase #5	$25.71	4.456%	$26.8556	$26.86	$26.85	$26.90
Purchase #6	$161.34	4.297%	$168.2728	$168.27	$168.25	$168.30
Purchase #7	$111.60	4.732%	$116.8809	$116.88	$116.90	$116.90
7 purchase totals =	$639.85		$689.4015	$689.40	$689.35	$689.50