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	$55.79	7.265%	$59.8431	$59.84	$59.85	$59.80
Purchase #2	$227.59	3.530%	$235.6239	$235.62	$235.60	$235.60
Purchase #3	$210.44	9.453%	$230.3329	$230.33	$230.35	$230.30
Purchase #4	$187.34	4.774%	$196.2836	$196.28	$196.30	$196.30
Purchase #5	$77.85	3.208%	$80.3474	$80.35	$80.35	$80.30
Purchase #6	$17.64	9.410%	$19.2999	$19.30	$19.30	$19.30
Purchase #7	$156.56	9.720%	$171.7776	$171.78	$171.80	$171.80
7 purchase totals =	$933.21		$993.5084	$993.50	$993.55	$993.40