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	$109.93	12.240%	$123.3854	$123.39	$123.40	$123.40
Purchase #2	$202.41	8.759%	$220.1391	$220.14	$220.15	$220.10
Purchase #3	$167.51	10.502%	$185.1019	$185.10	$185.10	$185.10
Purchase #4	$92.83	12.535%	$104.4662	$104.47	$104.45	$104.50
Purchase #5	$102.60	6.558%	$109.3285	$109.33	$109.35	$109.30
Purchase #6	$145.56	11.289%	$161.9923	$161.99	$162.00	$162.00
Purchase #7	$88.54	3.293%	$91.4556	$91.46	$91.45	$91.50
7 purchase totals =	$909.38		$995.8690	$995.88	$995.90	$995.90