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	$218.88	12.799%	$246.8945	$246.89	$246.90	$246.90
Purchase #2	$174.32	11.416%	$194.2204	$194.22	$194.20	$194.20
Purchase #3	$144.37	5.495%	$152.3031	$152.30	$152.30	$152.30
Purchase #4	$50.59	10.113%	$55.7062	$55.71	$55.70	$55.70
Purchase #5	$29.69	6.582%	$31.6442	$31.64	$31.65	$31.60
Purchase #6	$41.56	9.184%	$45.3769	$45.38	$45.40	$45.40
Purchase #7	$145.96	6.499%	$155.4459	$155.45	$155.45	$155.40
7 purchase totals =	$805.37		$881.5912	$881.59	$881.60	$881.50