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	$115.91	6.333%	$123.2506	$123.25	$123.25	$123.30
Purchase #2	$51.41	11.788%	$57.4702	$57.47	$57.45	$57.50
Purchase #3	$48.70	9.134%	$53.1483	$53.15	$53.15	$53.10
Purchase #4	$148.78	11.692%	$166.1754	$166.18	$166.20	$166.20
Purchase #5	$234.54	7.610%	$252.3885	$252.39	$252.40	$252.40
Purchase #6	$69.41	4.442%	$72.4932	$72.49	$72.50	$72.50
Purchase #7	$206.63	10.752%	$228.8469	$228.85	$228.85	$228.80
7 purchase totals =	$875.38		$953.7731	$953.78	$953.80	$953.80