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	$24.79	12.517%	$27.893	$27.89	$27.90	$27.90
Purchase #2	$212.46	11.253%	$236.3681	$236.37	$236.35	$236.40
Purchase #3	$115.69	7.833%	$124.752	$124.75	$124.75	$124.80
Purchase #4	$64.54	11.423%	$71.9124	$71.91	$71.90	$71.90
Purchase #5	$167.72	3.469%	$173.5382	$173.54	$173.55	$173.50
Purchase #6	$152.74	8.421%	$165.6022	$165.60	$165.60	$165.60
Purchase #7	$137.95	12.715%	$155.4903	$155.49	$155.50	$155.50
7 purchase totals =	$875.89		$955.5562	$955.55	$955.55	$955.60