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	$51.73	11.405%	$57.6298	$57.63	$57.65	$57.60
Purchase #2	$80.91	5.643%	$85.4758	$85.48	$85.50	$85.50
Purchase #3	$108.34	8.635%	$117.6952	$117.70	$117.70	$117.70
Purchase #4	$189.29	6.179%	$200.9862	$200.99	$201.00	$201.00
Purchase #5	$137.61	6.481%	$146.5285	$146.53	$146.55	$146.50
Purchase #6	$85.93	3.714%	$89.1214	$89.12	$89.10	$89.10
Purchase #7	$127.43	11.696%	$142.3342	$142.33	$142.35	$142.30
7 purchase totals =	$781.24		$839.7711	$839.78	$839.85	$839.70