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	$245.82	12.117%	$275.606	$275.61	$275.60	$275.60
Purchase #2	$188.56	4.375%	$196.8095	$196.81	$196.80	$196.80
Purchase #3	$7.50	7.119%	$8.0339	$8.03	$8.05	$8.00
Purchase #4	$38.85	10.313%	$42.8566	$42.86	$42.85	$42.90
Purchase #5	$22.92	12.825%	$25.8595	$25.86	$25.85	$25.90
Purchase #6	$44.37	5.820%	$46.9523	$46.95	$46.95	$47.00
Purchase #7	$200.72	12.408%	$225.6253	$225.63	$225.65	$225.60
7 purchase totals =	$748.74		$821.7431	$821.75	$821.75	$821.80