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	$165.59	9.253%	$180.912	$180.91	$180.90	$180.90
Purchase #2	$180.86	11.623%	$201.8814	$201.88	$201.90	$201.90
Purchase #3	$120.35	10.372%	$132.8327	$132.83	$132.85	$132.80
Purchase #4	$225.41	11.109%	$250.4508	$250.45	$250.45	$250.50
Purchase #5	$241.33	10.212%	$265.9746	$265.97	$265.95	$266.00
Purchase #6	$64.44	12.129%	$72.2559	$72.26	$72.25	$72.30
Purchase #7	$62.72	7.844%	$67.6398	$67.64	$67.65	$67.60
7 purchase totals =	$1,060.70		$1,171.9472	$1,171.94	$1,171.95	$1,172.00