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	$52.26	9.301%	$57.1207	$57.12	$57.10	$57.10
Purchase #2	$203.31	12.459%	$228.6404	$228.64	$228.65	$228.60
Purchase #3	$45.61	7.120%	$48.8574	$48.86	$48.85	$48.90
Purchase #4	$154.83	4.628%	$161.9955	$162.00	$162.00	$162.00
Purchase #5	$108.39	13.552%	$123.079	$123.08	$123.10	$123.10
Purchase #6	$75.65	9.328%	$82.7066	$82.71	$82.70	$82.70
Purchase #7	$85.56	6.247%	$90.9049	$90.90	$90.90	$90.90
7 purchase totals =	$725.61		$793.3045	$793.31	$793.30	$793.30