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	$120.67	13.854%	$137.3876	$137.39	$137.40	$137.40
Purchase #2	$14.84	3.370%	$15.3401	$15.34	$15.35	$15.30
Purchase #3	$201.37	13.389%	$228.3314	$228.33	$228.35	$228.30
Purchase #4	$103.46	5.789%	$109.4493	$109.45	$109.45	$109.40
Purchase #5	$66.77	8.843%	$72.6745	$72.67	$72.65	$72.70
Purchase #6	$236.52	5.756%	$250.1341	$250.13	$250.15	$250.10
Purchase #7	$83.97	3.260%	$86.7074	$86.71	$86.70	$86.70
7 purchase totals =	$827.60		$900.0244	$900.02	$900.05	$899.90