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	$129.58	7.318%	$139.0627	$139.06	$139.05	$139.10
Purchase #2	$207.63	7.618%	$223.4473	$223.45	$223.45	$223.40
Purchase #3	$152.39	12.420%	$171.3168	$171.32	$171.30	$171.30
Purchase #4	$160.78	8.528%	$174.4913	$174.49	$174.50	$174.50
Purchase #5	$76.72	11.221%	$85.3288	$85.33	$85.35	$85.30
Purchase #6	$79.98	13.465%	$90.7493	$90.75	$90.75	$90.70
Purchase #7	$41.92	4.159%	$43.6635	$43.66	$43.65	$43.70
7 purchase totals =	$849.00		$928.0597	$928.06	$928.05	$928.00