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	$43.27	5.830%	$45.7926	$45.79	$45.80	$45.80
Purchase #2	$37.31	5.731%	$39.4482	$39.45	$39.45	$39.40
Purchase #3	$145.95	12.722%	$164.5178	$164.52	$164.50	$164.50
Purchase #4	$14.59	8.337%	$15.8064	$15.81	$15.80	$15.80
Purchase #5	$57.76	7.234%	$61.9384	$61.94	$61.95	$61.90
Purchase #6	$223.71	11.393%	$249.1973	$249.20	$249.20	$249.20
Purchase #7	$143.48	8.740%	$156.0202	$156.02	$156.00	$156.00
7 purchase totals =	$666.07		$732.7209	$732.73	$732.70	$732.60