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	$206.82	3.214%	$213.4672	$213.47	$213.45	$213.50
Purchase #2	$103.53	11.597%	$115.5364	$115.54	$115.55	$115.50
Purchase #3	$220.97	10.771%	$244.7707	$244.77	$244.75	$244.80
Purchase #4	$64.57	12.815%	$72.8446	$72.84	$72.85	$72.80
Purchase #5	$64.76	10.217%	$71.3765	$71.38	$71.40	$71.40
Purchase #6	$139.74	3.692%	$144.8992	$144.90	$144.90	$144.90
Purchase #7	$202.71	6.269%	$215.4179	$215.42	$215.40	$215.40
7 purchase totals =	$1,003.10		$1,078.3125	$1,078.32	$1,078.30	$1,078.30