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	$5.85	5.443%	$6.1684	$6.17	$6.15	$6.20
Purchase #2	$130.86	6.454%	$139.3057	$139.31	$139.30	$139.30
Purchase #3	$39.92	5.151%	$41.9763	$41.98	$42.00	$42.00
Purchase #4	$84.50	6.294%	$89.8184	$89.82	$89.80	$89.80
Purchase #5	$227.30	11.540%	$253.5304	$253.53	$253.55	$253.50
Purchase #6	$153.43	11.824%	$171.5716	$171.57	$171.55	$171.60
Purchase #7	$81.53	8.205%	$88.2195	$88.22	$88.20	$88.20
7 purchase totals =	$723.39		$790.5903	$790.60	$790.55	$790.60