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	$247.69	3.306%	$255.8786	$255.88	$255.90	$255.90
Purchase #2	$207.74	6.649%	$221.5526	$221.55	$221.55	$221.60
Purchase #3	$27.46	10.758%	$30.4141	$30.41	$30.40	$30.40
Purchase #4	$156.53	5.747%	$165.5258	$165.53	$165.55	$165.50
Purchase #5	$19.42	7.679%	$20.9113	$20.91	$20.90	$20.90
Purchase #6	$225.76	8.721%	$245.4485	$245.45	$245.45	$245.40
Purchase #7	$54.40	8.463%	$59.0039	$59.00	$59.00	$59.00
7 purchase totals =	$939.00		$998.7348	$998.73	$998.75	$998.70