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	$131.92	5.469%	$139.1347	$139.13	$139.15	$139.10
Purchase #2	$131.73	12.553%	$148.2661	$148.27	$148.25	$148.30
Purchase #3	$39.92	12.681%	$44.9823	$44.98	$45.00	$45.00
Purchase #4	$78.52	13.858%	$89.4013	$89.40	$89.40	$89.40
Purchase #5	$109.51	13.351%	$124.1307	$124.13	$124.15	$124.10
Purchase #6	$85.43	13.279%	$96.7742	$96.77	$96.75	$96.80
Purchase #7	$208.97	4.110%	$217.5587	$217.56	$217.55	$217.60
7 purchase totals =	$786.00		$860.2480	$860.24	$860.25	$860.30