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	$40.56	4.289%	$42.2996	$42.30	$42.30	$42.30
Purchase #2	$12.88	8.272%	$13.9454	$13.95	$13.95	$13.90
Purchase #3	$37.91	4.369%	$39.5663	$39.57	$39.55	$39.60
Purchase #4	$222.53	6.144%	$236.2022	$236.20	$236.20	$236.20
Purchase #5	$40.64	10.866%	$45.0559	$45.06	$45.05	$45.10
Purchase #6	$41.25	6.391%	$43.8863	$43.89	$43.90	$43.90
Purchase #7	$219.41	9.208%	$239.6133	$239.61	$239.60	$239.60
7 purchase totals =	$615.18		$660.5690	$660.58	$660.55	$660.60