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	$38.87	9.457%	$42.5459	$42.55	$42.55	$42.50
Purchase #2	$55.64	10.515%	$61.4905	$61.49	$61.50	$61.50
Purchase #3	$160.83	6.123%	$170.6776	$170.68	$170.70	$170.70
Purchase #4	$35.75	11.270%	$39.779	$39.78	$39.80	$39.80
Purchase #5	$174.38	4.756%	$182.6735	$182.67	$182.65	$182.70
Purchase #6	$111.51	11.671%	$124.5243	$124.52	$124.50	$124.50
Purchase #7	$236.73	5.660%	$250.1289	$250.13	$250.15	$250.10
7 purchase totals =	$813.71		$871.8197	$871.82	$871.85	$871.80