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	$168.87	12.437%	$189.8724	$189.87	$189.85	$189.90
Purchase #2	$228.77	3.290%	$236.2965	$236.30	$236.30	$236.30
Purchase #3	$242.84	4.721%	$254.3045	$254.30	$254.30	$254.30
Purchase #4	$43.51	13.590%	$49.423	$49.42	$49.40	$49.40
Purchase #5	$235.38	6.556%	$250.8115	$250.81	$250.80	$250.80
Purchase #6	$90.70	5.656%	$95.83	$95.83	$95.85	$95.80
Purchase #7	$95.85	8.284%	$103.7902	$103.79	$103.80	$103.80
7 purchase totals =	$1,105.92		$1,180.3281	$1,180.32	$1,180.30	$1,180.30