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	$24.75	10.238%	$27.2839	$27.28	$27.30	$27.30
Purchase #2	$12.50	6.742%	$13.3428	$13.34	$13.35	$13.30
Purchase #3	$135.46	13.219%	$153.3665	$153.37	$153.35	$153.40
Purchase #4	$103.88	5.394%	$109.4833	$109.48	$109.50	$109.50
Purchase #5	$116.61	13.658%	$132.5366	$132.54	$132.55	$132.50
Purchase #6	$206.78	10.173%	$227.8157	$227.82	$227.80	$227.80
Purchase #7	$210.78	6.214%	$223.8779	$223.88	$223.90	$223.90
7 purchase totals =	$810.76		$887.7067	$887.71	$887.75	$887.70