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	$91.59	10.136%	$100.8736	$100.87	$100.85	$100.90
Purchase #2	$17.66	5.214%	$18.5808	$18.58	$18.60	$18.60
Purchase #3	$78.31	7.645%	$84.2968	$84.30	$84.30	$84.30
Purchase #4	$51.57	7.412%	$55.3924	$55.39	$55.40	$55.40
Purchase #5	$155.74	7.679%	$167.6993	$167.70	$167.70	$167.70
Purchase #6	$64.62	12.806%	$72.8952	$72.90	$72.90	$72.90
Purchase #7	$19.71	6.617%	$21.0142	$21.01	$21.00	$21.00
7 purchase totals =	$479.20		$520.7523	$520.75	$520.75	$520.80