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	$216.68	12.405%	$243.5592	$243.56	$243.55	$243.60
Purchase #2	$80.83	9.458%	$88.4749	$88.47	$88.45	$88.50
Purchase #3	$62.29	13.745%	$70.8518	$70.85	$70.85	$70.90
Purchase #4	$230.73	6.371%	$245.4298	$245.43	$245.45	$245.40
Purchase #5	$239.25	9.467%	$261.8998	$261.90	$261.90	$261.90
Purchase #6	$40.45	7.109%	$43.3256	$43.33	$43.35	$43.30
Purchase #7	$25.36	8.825%	$27.598	$27.60	$27.60	$27.60
7 purchase totals =	$895.59		$981.1391	$981.14	$981.15	$981.20