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	$155.36	10.238%	$171.2658	$171.27	$171.25	$171.30
Purchase #2	$53.48	11.124%	$59.4291	$59.43	$59.45	$59.40
Purchase #3	$179.63	5.372%	$189.2797	$189.28	$189.30	$189.30
Purchase #4	$117.92	12.135%	$132.2296	$132.23	$132.25	$132.20
Purchase #5	$28.93	8.591%	$31.4154	$31.42	$31.40	$31.40
Purchase #6	$70.27	3.208%	$72.5243	$72.52	$72.50	$72.50
Purchase #7	$79.82	13.476%	$90.5765	$90.58	$90.60	$90.60
7 purchase totals =	$685.41		$746.7204	$746.73	$746.75	$746.70