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	$121.93	5.251%	$128.3325	$128.33	$128.35	$128.30
Purchase #2	$132.91	11.571%	$148.289	$148.29	$148.30	$148.30
Purchase #3	$189.79	3.602%	$196.6262	$196.63	$196.65	$196.60
Purchase #4	$35.56	3.722%	$36.8835	$36.88	$36.90	$36.90
Purchase #5	$247.88	3.159%	$255.7105	$255.71	$255.70	$255.70
Purchase #6	$125.50	6.667%	$133.8671	$133.87	$133.85	$133.90
Purchase #7	$139.42	13.789%	$158.6446	$158.64	$158.65	$158.60
7 purchase totals =	$992.99		$1,058.3534	$1,058.35	$1,058.40	$1,058.30