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	$76.56	12.700%	$86.2831	$86.28	$86.30	$86.30
Purchase #2	$226.35	9.777%	$248.4802	$248.48	$248.50	$248.50
Purchase #3	$13.59	6.737%	$14.5056	$14.51	$14.50	$14.50
Purchase #4	$95.54	10.686%	$105.7494	$105.75	$105.75	$105.70
Purchase #5	$40.63	7.499%	$43.6768	$43.68	$43.70	$43.70
Purchase #6	$27.83	3.763%	$28.8772	$28.88	$28.90	$28.90
Purchase #7	$63.63	11.710%	$71.0811	$71.08	$71.10	$71.10
7 purchase totals =	$544.13		$598.6534	$598.66	$598.75	$598.70