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	$50.64	9.112%	$55.2543	$55.25	$55.25	$55.30
Purchase #2	$29.55	8.234%	$31.9831	$31.98	$32.00	$32.00
Purchase #3	$207.54	9.546%	$227.3518	$227.35	$227.35	$227.40
Purchase #4	$123.34	9.304%	$134.8156	$134.82	$134.80	$134.80
Purchase #5	$36.47	7.457%	$39.1896	$39.19	$39.20	$39.20
Purchase #6	$187.44	4.818%	$196.4709	$196.47	$196.45	$196.50
Purchase #7	$95.41	6.329%	$101.4485	$101.45	$101.45	$101.40
7 purchase totals =	$730.39		$786.5138	$786.51	$786.50	$786.60