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	$222.85	3.404%	$230.4358	$230.44	$230.45	$230.40
Purchase #2	$131.80	8.848%	$143.4617	$143.46	$143.45	$143.50
Purchase #3	$20.69	3.780%	$21.4721	$21.47	$21.45	$21.50
Purchase #4	$234.97	8.231%	$254.3104	$254.31	$254.30	$254.30
Purchase #5	$30.51	6.453%	$32.4788	$32.48	$32.50	$32.50
Purchase #6	$43.37	4.808%	$45.4552	$45.46	$45.45	$45.50
Purchase #7	$116.62	7.459%	$125.3187	$125.32	$125.30	$125.30
7 purchase totals =	$800.81		$852.9327	$852.94	$852.90	$853.00