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	$36.38	4.293%	$37.9418	$37.94	$37.95	$37.90
Purchase #2	$91.31	8.243%	$98.8367	$98.84	$98.85	$98.80
Purchase #3	$43.43	3.223%	$44.8297	$44.83	$44.85	$44.80
Purchase #4	$247.90	4.407%	$258.825	$258.83	$258.85	$258.80
Purchase #5	$169.79	9.342%	$185.6518	$185.65	$185.65	$185.70
Purchase #6	$220.76	6.163%	$234.3654	$234.37	$234.35	$234.40
Purchase #7	$46.85	7.701%	$50.4579	$50.46	$50.45	$50.50
7 purchase totals =	$856.42		$910.9083	$910.92	$910.95	$910.90