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	$91.39	8.523%	$99.1792	$99.18	$99.20	$99.20
Purchase #2	$237.52	9.224%	$259.4288	$259.43	$259.45	$259.40
Purchase #3	$179.96	10.702%	$199.2193	$199.22	$199.20	$199.20
Purchase #4	$73.90	11.115%	$82.114	$82.11	$82.10	$82.10
Purchase #5	$104.31	7.433%	$112.0634	$112.06	$112.05	$112.10
Purchase #6	$226.31	9.741%	$248.3549	$248.35	$248.35	$248.40
Purchase #7	$230.78	3.526%	$238.9173	$238.92	$238.90	$238.90
7 purchase totals =	$1,144.17		$1,239.2769	$1,239.27	$1,239.25	$1,239.30