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	$39.46	10.114%	$43.451	$43.45	$43.45	$43.50
Purchase #2	$147.96	7.807%	$159.5112	$159.51	$159.50	$159.50
Purchase #3	$222.58	6.468%	$236.9765	$236.98	$237.00	$237.00
Purchase #4	$26.55	3.119%	$27.3781	$27.38	$27.40	$27.40
Purchase #5	$110.39	8.212%	$119.4552	$119.46	$119.45	$119.50
Purchase #6	$148.91	7.851%	$160.6009	$160.60	$160.60	$160.60
Purchase #7	$247.65	9.258%	$270.5774	$270.58	$270.60	$270.60
7 purchase totals =	$943.50		$1,017.9503	$1,017.96	$1,018.00	$1,018.10