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	$137.79	9.199%	$150.4653	$150.47	$150.45	$150.50
Purchase #2	$64.59	3.874%	$67.0922	$67.09	$67.10	$67.10
Purchase #3	$28.47	5.142%	$29.9339	$29.93	$29.95	$29.90
Purchase #4	$93.64	6.260%	$99.5019	$99.50	$99.50	$99.50
Purchase #5	$224.53	6.315%	$238.7091	$238.71	$238.70	$238.70
Purchase #6	$115.91	10.295%	$127.8429	$127.84	$127.85	$127.80
Purchase #7	$144.31	13.653%	$164.0126	$164.01	$164.00	$164.00
7 purchase totals =	$809.24		$877.5579	$877.55	$877.55	$877.50