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	$113.46	10.450%	$125.3166	$125.32	$125.30	$125.30
Purchase #2	$61.83	7.469%	$66.4481	$66.45	$66.45	$66.40
Purchase #3	$126.80	11.537%	$141.4289	$141.43	$141.45	$141.40
Purchase #4	$133.77	6.117%	$141.9527	$141.95	$141.95	$142.00
Purchase #5	$89.85	13.783%	$102.234	$102.23	$102.25	$102.20
Purchase #6	$211.25	8.435%	$229.0689	$229.07	$229.05	$229.10
Purchase #7	$86.69	4.844%	$90.8893	$90.89	$90.90	$90.90
7 purchase totals =	$823.65		$897.3385	$897.34	$897.35	$897.30