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	$18.94	9.287%	$20.699	$20.70	$20.70	$20.70
Purchase #2	$199.51	3.792%	$207.0754	$207.08	$207.10	$207.10
Purchase #3	$85.43	5.709%	$90.3072	$90.31	$90.30	$90.30
Purchase #4	$51.56	9.135%	$56.27	$56.27	$56.25	$56.30
Purchase #5	$35.44	6.429%	$37.7184	$37.72	$37.70	$37.70
Purchase #6	$239.85	10.356%	$264.6889	$264.69	$264.70	$264.70
Purchase #7	$215.72	13.744%	$245.3686	$245.37	$245.35	$245.40
7 purchase totals =	$846.45		$922.1275	$922.14	$922.10	$922.20