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	$29.94	11.356%	$33.34	$33.34	$33.35	$33.30
Purchase #2	$165.46	11.706%	$184.8287	$184.83	$184.85	$184.80
Purchase #3	$165.63	9.131%	$180.7537	$180.75	$180.75	$180.80
Purchase #4	$42.71	11.466%	$47.6071	$47.61	$47.60	$47.60
Purchase #5	$41.46	3.726%	$43.0048	$43.00	$43.00	$43.00
Purchase #6	$157.70	5.864%	$166.9475	$166.95	$166.95	$166.90
Purchase #7	$43.94	6.780%	$46.9191	$46.92	$46.90	$46.90
7 purchase totals =	$646.84		$703.4009	$703.40	$703.40	$703.30