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	$38.94	12.648%	$43.8651	$43.87	$43.85	$43.90
Purchase #2	$179.59	11.841%	$200.8553	$200.86	$200.85	$200.90
Purchase #3	$100.81	5.607%	$106.4624	$106.46	$106.45	$106.50
Purchase #4	$174.96	12.125%	$196.1739	$196.17	$196.15	$196.20
Purchase #5	$147.95	3.496%	$153.1223	$153.12	$153.10	$153.10
Purchase #6	$106.88	13.371%	$121.1709	$121.17	$121.15	$121.20
Purchase #7	$21.70	8.830%	$23.6161	$23.62	$23.60	$23.60
7 purchase totals =	$770.83		$845.2660	$845.27	$845.15	$845.40