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	$5.69	13.843%	$6.4777	$6.48	$6.50	$6.50
Purchase #2	$121.85	5.729%	$128.8308	$128.83	$128.85	$128.80
Purchase #3	$138.73	3.523%	$143.6175	$143.62	$143.60	$143.60
Purchase #4	$152.63	10.375%	$168.4654	$168.47	$168.45	$168.50
Purchase #5	$37.77	7.623%	$40.6492	$40.65	$40.65	$40.60
Purchase #6	$198.74	4.427%	$207.5382	$207.54	$207.55	$207.50
Purchase #7	$38.73	9.240%	$42.3087	$42.31	$42.30	$42.30
7 purchase totals =	$694.14		$737.8875	$737.90	$737.90	$737.80