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	$37.53	3.361%	$38.7914	$38.79	$38.80	$38.80
Purchase #2	$82.51	7.690%	$88.855	$88.86	$88.85	$88.90
Purchase #3	$184.43	5.338%	$194.2749	$194.27	$194.25	$194.30
Purchase #4	$182.97	7.535%	$196.7568	$196.76	$196.75	$196.80
Purchase #5	$38.44	13.599%	$43.6675	$43.67	$43.65	$43.70
Purchase #6	$48.94	13.783%	$55.6854	$55.69	$55.70	$55.70
Purchase #7	$213.47	11.665%	$238.3713	$238.37	$238.35	$238.40
7 purchase totals =	$788.29		$856.4023	$856.41	$856.35	$856.60