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	$133.25	9.752%	$146.2445	$146.24	$146.25	$146.20
Purchase #2	$137.65	6.241%	$146.2407	$146.24	$146.25	$146.20
Purchase #3	$71.67	10.108%	$78.9144	$78.91	$78.90	$78.90
Purchase #4	$54.56	3.649%	$56.5509	$56.55	$56.55	$56.60
Purchase #5	$16.75	3.846%	$17.3942	$17.39	$17.40	$17.40
Purchase #6	$54.35	13.818%	$61.8601	$61.86	$61.85	$61.90
Purchase #7	$248.34	5.233%	$261.3356	$261.34	$261.35	$261.30
7 purchase totals =	$716.57		$768.5404	$768.53	$768.55	$768.50