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	$31.27	9.353%	$34.1947	$34.19	$34.20	$34.20
Purchase #2	$64.27	6.557%	$68.4842	$68.48	$68.50	$68.50
Purchase #3	$98.34	13.786%	$111.8972	$111.90	$111.90	$111.90
Purchase #4	$37.97	11.854%	$42.471	$42.47	$42.45	$42.50
Purchase #5	$164.61	10.232%	$181.4529	$181.45	$181.45	$181.50
Purchase #6	$141.45	12.706%	$159.4226	$159.42	$159.40	$159.40
Purchase #7	$37.45	11.715%	$41.8373	$41.84	$41.85	$41.80
7 purchase totals =	$575.36		$639.7599	$639.75	$639.75	$639.80