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	$31.36	8.859%	$34.1382	$34.14	$34.15	$34.10
Purchase #2	$194.69	11.657%	$217.385	$217.39	$217.40	$217.40
Purchase #3	$209.55	4.440%	$218.854	$218.85	$218.85	$218.90
Purchase #4	$63.96	6.316%	$67.9997	$68.00	$68.00	$68.00
Purchase #5	$84.25	7.192%	$90.3093	$90.31	$90.30	$90.30
Purchase #6	$236.96	7.761%	$255.3505	$255.35	$255.35	$255.40
Purchase #7	$219.83	10.729%	$243.4156	$243.42	$243.40	$243.40
7 purchase totals =	$1,040.60		$1,127.4523	$1,127.46	$1,127.45	$1,127.50