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	$7.42	10.133%	$8.1719	$8.17	$8.15	$8.20
Purchase #2	$250.34	10.804%	$277.3867	$277.39	$277.40	$277.40
Purchase #3	$117.71	8.239%	$127.4081	$127.41	$127.40	$127.40
Purchase #4	$40.30	12.464%	$45.323	$45.32	$45.30	$45.30
Purchase #5	$162.45	7.344%	$174.3803	$174.38	$174.40	$174.40
Purchase #6	$224.27	4.402%	$234.1424	$234.14	$234.15	$234.10
Purchase #7	$165.32	12.236%	$185.5486	$185.55	$185.55	$185.50
7 purchase totals =	$967.81		$1,052.3610	$1,052.36	$1,052.35	$1,052.30