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	$46.55	12.364%	$52.3054	$52.31	$52.30	$52.30
Purchase #2	$208.57	12.441%	$234.5182	$234.52	$234.50	$234.50
Purchase #3	$194.86	10.425%	$215.1742	$215.17	$215.15	$215.20
Purchase #4	$28.30	12.458%	$31.8256	$31.83	$31.85	$31.80
Purchase #5	$51.98	9.302%	$56.8152	$56.82	$56.80	$56.80
Purchase #6	$96.53	4.230%	$100.6132	$100.61	$100.60	$100.60
Purchase #7	$173.26	4.687%	$181.3807	$181.38	$181.40	$181.40
7 purchase totals =	$800.05		$872.6325	$872.64	$872.60	$872.60