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	$218.69	7.702%	$235.5335	$235.53	$235.55	$235.50
Purchase #2	$87.42	4.846%	$91.6564	$91.66	$91.65	$91.70
Purchase #3	$166.65	11.524%	$185.8547	$185.85	$185.85	$185.90
Purchase #4	$233.83	5.151%	$245.8746	$245.87	$245.85	$245.90
Purchase #5	$141.39	9.847%	$155.3127	$155.31	$155.30	$155.30
Purchase #6	$80.88	11.859%	$90.4716	$90.47	$90.45	$90.50
Purchase #7	$215.27	9.338%	$235.3719	$235.37	$235.35	$235.40
7 purchase totals =	$1,144.13		$1,240.0754	$1,240.06	$1,240.00	$1,240.20