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	$132.73	6.145%	$140.8863	$140.89	$140.90	$140.90
Purchase #2	$152.60	9.492%	$167.0848	$167.08	$167.10	$167.10
Purchase #3	$120.63	6.473%	$128.4384	$128.44	$128.45	$128.40
Purchase #4	$225.59	10.419%	$249.0942	$249.09	$249.10	$249.10
Purchase #5	$230.45	11.520%	$256.9978	$257.00	$257.00	$257.00
Purchase #6	$73.77	13.573%	$83.7828	$83.78	$83.80	$83.80
Purchase #7	$67.65	9.182%	$73.8616	$73.86	$73.85	$73.90
7 purchase totals =	$1,003.42		$1,100.1459	$1,100.14	$1,100.20	$1,100.20