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	$67.30	9.300%	$73.5589	$73.56	$73.55	$73.60
Purchase #2	$71.96	6.854%	$76.8921	$76.89	$76.90	$76.90
Purchase #3	$40.37	3.117%	$41.6283	$41.63	$41.65	$41.60
Purchase #4	$209.32	7.708%	$225.4544	$225.45	$225.45	$225.50
Purchase #5	$245.96	12.790%	$277.4183	$277.42	$277.40	$277.40
Purchase #6	$137.41	3.763%	$142.5807	$142.58	$142.60	$142.60
Purchase #7	$237.34	9.675%	$260.3026	$260.30	$260.30	$260.30
7 purchase totals =	$1,009.66		$1,097.8353	$1,097.83	$1,097.85	$1,097.90