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	$123.47	9.221%	$134.8552	$134.86	$134.85	$134.90
Purchase #2	$151.88	3.398%	$157.0409	$157.04	$157.05	$157.00
Purchase #3	$229.27	8.541%	$248.852	$248.85	$248.85	$248.90
Purchase #4	$80.31	12.358%	$90.2347	$90.23	$90.25	$90.20
Purchase #5	$202.85	11.170%	$225.5083	$225.51	$225.50	$225.50
Purchase #6	$75.89	10.221%	$83.6467	$83.65	$83.65	$83.60
Purchase #7	$192.35	12.369%	$216.1418	$216.14	$216.15	$216.10
7 purchase totals =	$1,056.02		$1,156.2796	$1,156.28	$1,156.30	$1,156.20