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	$82.60	9.841%	$90.7287	$90.73	$90.75	$90.70
Purchase #2	$147.42	12.175%	$165.3684	$165.37	$165.35	$165.40
Purchase #3	$169.29	7.242%	$181.55	$181.55	$181.55	$181.60
Purchase #4	$135.41	8.526%	$146.9551	$146.96	$146.95	$147.00
Purchase #5	$219.58	11.335%	$244.4694	$244.47	$244.45	$244.50
Purchase #6	$73.50	10.634%	$81.316	$81.32	$81.30	$81.30
Purchase #7	$78.96	12.555%	$88.8734	$88.87	$88.85	$88.90
7 purchase totals =	$906.76		$999.2610	$999.27	$999.20	$999.40