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	$31.45	12.133%	$35.2658	$35.27	$35.25	$35.30
Purchase #2	$166.47	4.588%	$174.1076	$174.11	$174.10	$174.10
Purchase #3	$50.77	5.229%	$53.4248	$53.42	$53.40	$53.40
Purchase #4	$38.94	9.466%	$42.6261	$42.63	$42.65	$42.60
Purchase #5	$196.52	6.450%	$209.1955	$209.20	$209.20	$209.20
Purchase #6	$167.25	10.868%	$185.4267	$185.43	$185.45	$185.40
Purchase #7	$88.42	3.145%	$91.2008	$91.20	$91.20	$91.20
7 purchase totals =	$739.82		$791.2473	$791.26	$791.25	$791.20