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	$19.27	3.240%	$19.8943	$19.89	$19.90	$19.90
Purchase #2	$135.31	4.608%	$141.5451	$141.55	$141.55	$141.50
Purchase #3	$187.82	5.144%	$197.4815	$197.48	$197.50	$197.50
Purchase #4	$75.45	13.402%	$85.5618	$85.56	$85.55	$85.60
Purchase #5	$86.43	3.287%	$89.271	$89.27	$89.25	$89.30
Purchase #6	$60.40	5.469%	$63.7033	$63.70	$63.70	$63.70
Purchase #7	$11.39	6.427%	$12.122	$12.12	$12.10	$12.10
7 purchase totals =	$576.07		$609.5790	$609.57	$609.55	$609.60