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	$25.96	4.501%	$27.1285	$27.13	$27.15	$27.10
Purchase #2	$143.80	6.336%	$152.9112	$152.91	$152.90	$152.90
Purchase #3	$47.79	13.447%	$54.2163	$54.22	$54.20	$54.20
Purchase #4	$199.71	3.126%	$205.9529	$205.95	$205.95	$206.00
Purchase #5	$227.73	7.787%	$245.4633	$245.46	$245.45	$245.50
Purchase #6	$51.50	6.269%	$54.7285	$54.73	$54.75	$54.70
Purchase #7	$233.75	12.435%	$262.8168	$262.82	$262.80	$262.80
7 purchase totals =	$930.24		$1,003.2175	$1,003.22	$1,003.20	$1,003.20