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	$32.37	3.616%	$33.5405	$33.54	$33.55	$33.50
Purchase #2	$47.95	9.428%	$52.4707	$52.47	$52.45	$52.50
Purchase #3	$190.78	7.420%	$204.9359	$204.94	$204.95	$204.90
Purchase #4	$243.56	13.271%	$275.8828	$275.88	$275.90	$275.90
Purchase #5	$205.63	4.248%	$214.3652	$214.37	$214.35	$214.40
Purchase #6	$163.83	10.121%	$180.4112	$180.41	$180.40	$180.40
Purchase #7	$114.44	12.638%	$128.9029	$128.90	$128.90	$128.90
7 purchase totals =	$998.56		$1,090.5092	$1,090.51	$1,090.50	$1,090.50